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TerraMaster F2-221 NAS Backplane Pinout Notes

Mon, 04 May 2026 06:02:56 +0800

This note documents the non-standard backplane connector pinout of the TerraMaster F2-221 NAS. The connector looks close to a PCIe edge connector, but it is not a standard PCIe slot. It is a custom TerraMaster backplane interface.

The connector carries SATA, power, reset, and PCIe signals at the same time. Once PCIe1 x1 is confirmed usable, a custom backplane can expose an M.2 M-key slot and use an NVMe SSD as an internal system drive.

The same idea also applies to the TerraMaster F2-220. Although the F2-220 and F2-221 use different platforms, a fnNAS forum test shows that F3 Backplane V1.1 can detect NVMe on the F2-220, and the NVMe drive is visible inside the OS installer. The extra work is that the old BIOS may not support booting from NVMe.

Summary

The F2-221 backplane connector contains:

Signals for two native SATA ports
12V, 5V, 3.3V, and GND
SATA drive power-control related signals
PERST#
At least one usable PCIe Gen2 x1 signal group
Partial clues for a second PCIe signal group, but not fully verified

PCIe1 can be used to expose an M.2 M-key NVMe slot. In testing, the NVMe drive runs at PCIe Gen2 x1, and the BIOS can detect and boot from it.

F2-220 testing points in the same direction: the hardware can detect NVMe, but the BIOS boot stage may require injecting an NVMe module, and the boot entry may appear as PATA.

Backplane Connector Pinout

The connector has B/A sides. ? means unknown or unconnected, and NC means not connected.

Pin	B side	A side
1	12V	?
2	12V	12V
3	12V	12V
4	GND	GND
5	SATA1 A+	SATA1 B+
6	SATA1 A-	SATA1 B-
7	GND	NC
8	5V	5V
9	5V	5V
10	?	5V
11	?	?
12	3.3V	GND
13	GND	3.3V
14	SATA2 A+	3.3V
15	SATA2 A-	GND
16	GND	SATA2 B+
17	PERST#	SATA2 B-
18	GND	GND
19	PCIe1 TX+	NC
20	PCIe1 TX-	GND
21	GND	PCIe1 RX+
22	GND	PCIe1 RX-
23	PCIe1 REFCLK+	GND
24	PCIe1 REFCLK-	GND
25	GND	PCIe2 RX+
26	GND	PCIe2 RX-
27	PCIe2 TX+	GND
28	PCIe2 TX-	GND
29	GND	PCIe2 REFCLK+
30	?	PCIe2 REFCLK-
31	?	GND
32	GND	?

PCIe1 has higher practical reference value. PCIe2 is not fully verified and should only be treated as a clue, not a reliable design basis.

Signal Source Reasoning

The stock F2-221 dual-bay backplane does not include a PCIe-to-SATA controller. SATA signals go directly from the motherboard connector into the backplane. The extra PCIe signals are mainly inferred from other multi-bay models in the same product family.

The TerraMaster F5-422 backplane uses two ASMedia ASM1061 chips. ASM1061 is a PCIe Gen2 x1 to dual-SATA controller. Combined with the Intel J3355 having 2 SATA ports and 6 PCIe Gen2 lanes, this suggests that multi-bay models expand SATA ports through PCIe.

Therefore, it is reasonable for the F2-221 motherboard connector to retain PCIe signals. The vendor likely reuses motherboard designs across models with different bay counts and changes functionality through the backplane.

PCIe Differential Pair Identification

PCIe differential pairs often go into inner layers after vias, so photos alone cannot trace the complete routing. One useful rule is that, in traditional PCIe designs, TX differential pairs usually have AC coupling capacitors.

The direction must be viewed in reverse:

TX from the ASM1061 controller’s perspective corresponds to RX on the CPU or motherboard side.
RX from the ASM1061 controller’s perspective corresponds to TX on the CPU or motherboard side.
REFCLK needs to be judged together with neighboring differential pairs and routing location.

This kind of pinout is better treated as hardware reverse-engineering material, not as an official specification.

Validation

F3 Backplane designs based on this pinout have completed the following validation:

The original two SATA drive bays remain usable.
PCIe1 can be routed to an M.2 M-key slot.
The NVMe SSD can be detected by BIOS.
The NAS can boot directly from the NVMe SSD.
btrfs scrub found no disk errors.
The system ran from the NVMe SSD for weeks without obvious issues.

The test NVMe SSD was a Patriot P300 128GB. hdparm result:

1
2
3

/dev/nvme0n1:
 Timing cached reads:   4554 MB in  2.00 seconds = 2279.68 MB/sec
 Timing buffered disk reads: 1222 MB in  3.00 seconds = 407.22 MB/sec

This speed matches the PCIe Gen2 x1 limitation. The goal is not to fully utilize NVMe performance, but to replace an external USB SSD with an internal system drive.

Notes

This pinout is useful as a reference for hardware reverse engineering and custom backplanes, but it should not be treated as official documentation.

The connector is not standard PCIe and cannot directly accept generic PCIe devices.
? pins are unverified and should not be connected to critical circuits casually.
PCIe2 is not fully verified and carries higher risk than PCIe1.
CLKREQ is not fully routed like a normal M.2 design, so ASPM may not work.
SATA power includes hot-swap related load switch and slow start logic; do not route only signal lines while ignoring power control.
If reproducing the design, measure your own motherboard and backplane again instead of relying only on photos.

Original project write-up: I made a new backplane for my Terramaster F2-221 NAS
F3 Backplane KiCad project: arnarg/f3_backplane
F3 Backplane pinout CSV: f3_backplane.csv
F2-220 compatibility test: 铁威马F2-220折腾飞牛OS过程

CRPS Common Redundant Server Power Supply Standard, Pin Functions, and Common Models

Fri, 17 Apr 2026 08:49:20 +0800

CRPS stands for Common Redundant Power Supply. It is mainly used in servers, storage systems, switches, AI servers, and industrial computing equipment to standardize the form factor, card-edge connector, management signals, and firmware behavior of hot-plug redundant power supply modules.

Compared with a common ATX power supply, CRPS has several clear characteristics:

Modular hot-plug design, suitable for 1+1, 2+1, and N+1 redundancy.
The main output is usually a single 12V rail, and the motherboard or PDB converts it to the voltages required by CPUs, memory, drives, and fans.
It uses a 2x25 card-edge connector, commonly 50 pins.
It supports PMBus / SMBus / I2C management for reading voltage, current, temperature, alarms, and FRU information.
It supports server PSU features such as current sharing, remote sense, PSON power-on control, and PWOK status output.

Early CRPS designs were mainly promoted by Intel. Later, the form factor evolved into OCP M-CRPS, or Modular Hardware System - Common Redundant Power Supply. Today many vendors use terms such as CRPS, M-CRPS, Intel standard CRPS form factor, or OCP M-CRPS in their documentation. In actual use, pay attention to the details: two supplies both called CRPS may still differ in power rating, length, width, airflow direction, firmware, and available signals.

CRPS vs CSPS

The previous article covered CSPS / Common Slot, which is commonly seen in the earlier HP / HPE server ecosystem and typically uses a 64 pin card-edge connector. CRPS is closer to the Intel / OCP ecosystem, and its typical connector is 2x25, or 50 pins total.

A simple comparison:

Item	CSPS / Common Slot	CRPS / M-CRPS
Common ecosystem	HP / HPE Common Slot	Intel CRPS, OCP M-CRPS, multi-vendor servers
Common connector	64 pin card edge	2x25 card edge, 50 pins
Main output	12V	12V
Management interface	PMBus / SMBus	PMBus / SMBus
Interchangeability	More vendor-ecosystem oriented	More focused on cross-platform standardization
Notes	Different HP generations may still differ	CRPS and M-CRPS still require size and signal verification

So CRPS and CSPS should not be mixed casually. They may both be hot-plug 12V server power supplies, but their gold-finger count, mechanical structure, and signal definitions are different.

Standard 2x25 Edge Connector Pinout

The following is a common 2x25 CRPS pinout seen in many PSU documents. Different vendors may rename some signals as SMART_ON, CR_BUS#, PS_KILL, VIN_GOOD, and so on, but the general structure is usually similar.

Pin	A-side definition	B-side definition
1	`GND`	`GND`
2	`GND`	`GND`
3	`GND`	`GND`
4	`GND`	`GND`
5	`GND`	`GND`
6	`GND`	`GND`
7	`GND`	`GND`
8	`GND`	`GND`
9	`GND`	`GND`
10	`+12V`	`+12V`
11	`+12V`	`+12V`
12	`+12V`	`+12V`
13	`+12V`	`+12V`
14	`+12V`	`+12V`
15	`+12V`	`+12V`
16	`+12V`	`+12V`
17	`+12V`	`+12V`
18	`+12V`	`+12V`
19	`PMBus_SDA`	`A0` / SMBus address bit
20	`PMBus_SCL`	`A1` / SMBus address bit
21	`PSON#`	`+12VSB`
22	`SMBAlert#`	`SMART_ON` / `CR_BUS#`
23	`+12V_Return Sense`	`+12V_Share Bus#` / Load Share
24	`+12V_Remote Sense`	`PRESENT#`
25	`PWOK`	`NC` / `VIN_GOOD` / `PS_KILL` optional

A1-A9 and B1-B9 are ground. A10-A18 and B10-B18 are the main 12V output. In other words, the high-current main output has 18 contacts for 12V and 18 contacts for GND. The remaining A19-A25 and B19-B25 pins are used for management, control, sense, and status signals.

Pin Function Notes

High-Current Output

+12V is the main output and is usually present after the supply is enabled. CRPS power ratings commonly range from 550W, 800W, and 1300W to 1600W, 2000W, 2400W, 3000W, or even 3200W.

At 12V, that roughly means:

800W is about 66.7A.
1300W is about 108A.
1600W is about 133A.
2400W is about 200A.
3200W is about 267A.

This level of current cannot be carried by only a few contacts or thin wires. When designing a PDB or breakout board, all +12V and GND contacts should participate in current sharing, with large copper pours, copper bars, heavy-copper PCBs, or multilayer parallel structures.

`+12VSB`

+12VSB is the standby 12V output. As long as input power is present, it is usually available even before the main 12V output is enabled. It powers the BMC, management controller, power-on control circuit, PMBus pull-up resistors, or standby logic.

Do not treat +12VSB as the main output. Its current capability is usually much lower than the main 12V rail. Common values include 1A, 2A, and 2.5A, but the exact value depends on the PSU documentation.

`PSON#`

PSON# is the main output power-on control pin and is active low. A common method is to pull PSON# to ground through an open-drain output, MOSFET, or transistor, causing the PSU to enter the working state and enable the main 12V output.

For temporary testing, you can pull PSON# down to GND through a resistor, for example in the 1kΩ to 10kΩ range for a lower-risk first test. Do not immediately hard-short unfamiliar signal pins.

`PWOK`

PWOK is the Power OK status signal. After the main 12V output becomes stable, the PSU uses this signal to tell the system that the output is valid. The motherboard or PDB can use it as a power-sequencing condition.

If PSON# is already pulled low but PWOK does not change, check input voltage, load, protection state, PRESENT#, remote sense, and PMBus alarms.

`PMBus_SDA` / `PMBus_SCL`

These two pins are the PMBus / SMBus management bus, used to read or control PSU status. Common uses include:

Reading output voltage, current, and input power.
Reading temperature, fan speed, alarms, and fault status.
Reading vendor, model, serial number, and FRU information.
Working with the BMC for power capping, alarm logging, and redundancy policies.

Although PMBus is based on SMBus / I2C, its command set, address, and electrical levels must follow the specific PSU documentation. Do not assume it can be connected directly to a 5V I2C bus.

`A0` / `A1`

A0 and A1 are commonly used to set the SMBus address. In a redundant multi-PSU system, each PSU module needs a different address so the BMC can identify PSU1, PSU2, PSU3, and so on.

Many power supplies have internal pull-ups on the address pins. The PDB pulls them low or leaves them floating according to the slot position, which determines the address combination.

`SMBAlert#`

SMBAlert# is the SMBus alert signal and is usually active low. When a temperature, input, output, fan, or protection-related event occurs, the PSU can use this signal to ask the BMC to read PMBus status.

`SMART_ON` / `CR_BUS#`

This signal is not named consistently across documents. Common names include SMART_ON, CR_BUS#, and Wake up Bus. It is related to redundancy, PSU sleep, and cold redundancy.

At low load, the system can let some redundant power supplies enter a lower-power state while only the necessary supplies carry the load. When load increases or one PSU becomes abnormal, the system wakes the other modules. This type of feature usually requires coordination among the PDB, BMC, and PSU firmware, so it is not recommended to drive it casually on a simple DIY breakout board.

`+12V Remote Sense` / `+12V Return Sense`

These two pins are remote sense lines, used to compensate for cable and copper loss between the PSU and the load.

+12V Remote Sense connects to the 12V sense point at the load end.
+12V Return Sense connects to the ground / return sense point at the load end.

If the PSU requires remote sense and the breakout board does not handle it correctly, the output voltage may be inaccurate, or the supply may enter protection or fail to start. A simple breakout board usually ties the sense lines to local 12V / GND according to the documentation, but avoid creating a wrong path where a thin sense wire carries high current.

`+12V Share Bus#`

+12V Share Bus#, or Load Share, is the parallel current-sharing signal. When multiple CRPS modules are paralleled, the supplies coordinate current sharing through this signal so that one module does not carry too much load for a long time.

For single-PSU use, this signal usually does not need to be involved in main output testing. For multi-PSU parallel operation, it must be handled according to the PSU and PDB documentation. Do not simply hard-parallel the 12V outputs and run them at full load.

`PRESENT#`

PRESENT# is the PSU presence-detect signal and is usually active low. The PDB or motherboard uses it to determine whether a PSU module is inserted in the slot.

Some power supplies may need PRESENT# to be handled correctly before entering the expected working state. When testing an unfamiliar CRPS module, first confirm the default level of PRESENT# and whether it needs to be tied to ground.

`VIN_GOOD` / `PS_KILL` / `NC`

B25 varies across documents. Some mark it as NC, some use it as VIN_GOOD, and some mention optional PS_KILL. Therefore this pin should not be wired based on experience from only one model.

For a generic breakout board, it is better to bring B25 out separately and leave a test point. Do not connect it to ground or 12V by default.

Basic Approach to Starting a CRPS PSU

For standalone testing, the following sequence reduces risk:

Do not connect the main load. Apply only AC input and check whether +12VSB is present.
Confirm the A/B side orientation and identify GND, PSON#, PRESENT#, and PWOK.
Pull PSON# down to GND through a resistor and check whether the main +12V output appears.
Add a small load, such as a 12V bulb, resistor load, or electronic load.
Increase the load gradually while watching output voltage, fan behavior, temperature rise, and protection behavior.
If monitoring is needed, connect PMBus after confirming voltage levels, address, and pull-ups.

If the PSU shuts down a few seconds after starting, common causes include:

No minimum load.
Incorrect handling of PRESENT# or remote sense.
Insufficient input voltage, with power derating at low-line input.
Fan, temperature, overcurrent, or overvoltage protection.
PMBus / BMC expected status signals are not satisfied.

Breakout Board Design Notes

A CRPS breakout board may look like it is just bringing out 12V, but the real difficulty is high current and reliability.

Recommendations:

Use a card-edge connector with the proper current rating, such as the common 2x25 CRPS connector seen in datasheets.
Use large copper pours, heavy copper, multilayer parallel planes, copper bars, or stud outputs for +12V and GND.
Make every high-current contact participate in current sharing. Do not connect only a few pins.
Handle sense lines separately and keep them away from the main current path.
Control PSON# with an open-drain output or MOSFET. Do not let an MCU hard-pull an unknown signal directly.
Keep ground reference and test points near PMBus_SDA / PMBus_SCL.
Add fuses, breakers, TVS devices, or electronic protection on the output. At minimum, have a clear short-circuit protection strategy.
High-power modules require proper airflow. Do not let a server PSU run at full load for a long time in a small box with no airflow.

Common CRPS / M-CRPS Models and Series

The following table lists common CRPS / M-CRPS models, series, and power ranges found in documentation. When buying used modules, still check the nameplate, connector, length, airflow direction, and PDB compatibility.

Vendor / Series	Common models / power	Notes
Intel CRPS	`FXX460GCRPS`, `FXX750PCRPS`, `FXX1200PCRPS`, `FXX1600PCRPS`	Common CRPS options for Intel server platforms, covering 460W, 750W, 1200W, and 1600W
Bel Power Solutions	`PEC800-12-074xA`, `TEC800`, `TEC1300`, `TEC1600`, `TEC2000`	Common CRPS front-end supplies; documentation clearly provides a 2x25 pinout
Advanced Energy / Artesyn	`CSU1300AP`, `CSU1800AP`, etc.	Data-center / server PSU modules, commonly 1300W and 1800W
Lite-On	`RPG800-12AS`, `RPG1300-12AS`, 1600W CRPS series	Lite-On CRPS product line for data centers, cloud computing, and AI servers
FSP	`FSP1600-20HM`, `FSP2400-22HM`, `FSP550-20FM`, `FSP800-20FM`, `FSP2000-20FM`, `FSP2400-20FM`	FSP CRPS / M-CRPS modules, commonly 550W to 2400W
Compuware	`CPR-8011-3M1`, MCRPS 1200W / 1600W / 2200W / 3200W	Supports PMBus, redundancy, and current sharing; MCRPS targets AI and OCP data centers
MORNSUN	`LMS800-P12BG`, `LMS1600-P12B`, `LMS2000-P12B`	Chinese CRPS modules; documentation lists the 2x25 edge connector pinout
Delta	`DPS-1200AB-4D` and other CRPS modules	Delta has many server PSUs; verify whether the unit is really a CRPS 50 pin form factor before buying
HPE M-CRPS	`P73190-B21` 800W, `P67240-B21` 1000W, `P67244-B21` 1500W, `P67252-B21` 2400W, `P67248-B21` 3200W	Gen12 platform M-CRPS; HPE explicitly marks them as OCP-compliant. There are also -48VDC models `P82412-B21` and `P73210-B21`
Generic white-label / industrial brands	550W, 800W, 1200W, 1300W, 1600W, 2000W, 2400W, 2600W, 3000W	Many products are labeled CRPS, but verify whether they really use the standard 2x25 connector

How to Judge Compatibility Before Buying or Reusing

When you get a hot-plug server PSU, do not rely only on its appearance or on a seller title that says CRPS. Check the following:

Whether the card edge is 2x25, 50 pins total.
Whether A1-A9 / B1-B9 are GND, and A10-A18 / B10-B18 are 12V.
Whether A19-A25 / B19-B25 match the PMBus, PSON, 12VSB, Sense, PRESENT, and PWOK signal layout.
Whether the PSU can deliver its rated power at your input voltage. Many high-power CRPS supplies derate at 100-127V low-line input.
Whether it needs a PDB, BMC, or PMBus command to enter the full operating mode.
Whether the airflow direction fits your chassis.
Whether it supports the redundancy mode you need, such as 1+1, N+1, cold redundancy, or current sharing.

Summary

The core points of CRPS are:

It is a standardized redundant server PSU module.
The typical connector is a 2x25, 50 pin card edge.
The main output is high-current 12V, with a separate 12VSB standby supply.
PSON# controls the main output, and PWOK indicates valid output.
PMBus provides monitoring and management.
Sense and Share Bus make it suitable for high-current, redundant, and parallel operation.

If you only want a lab 12V supply, at minimum you need to understand GND, +12V, +12VSB, PSON#, PRESENT#, and PWOK. If you want a truly reliable PDB or multi-PSU parallel system, you must also handle remote sense, current sharing, PMBus, airflow, and protection carefully.

References

CSPS Common Slot Server Power Supply Interface and Pinout

Thu, 16 Apr 2026 23:11:04 +0800

CSPS here refers to Common Slot Server Power Supply, also often called Common Slot Power Supply. These power supplies are common on HP / HPE ProLiant server platforms. Their typical characteristics are:

Modular hot-plug power supply form factor.
Mainly 12V output, suitable for centralized server backplane power distribution.
64 pin edge connector / gold finger interface to the backplane.
In addition to high-current 12V and GND, they also provide 12VSB standby power, enable signals, status signals, and a PMBus / SMBus / I2C management interface.

These power supplies are common on the used market, such as DPS-750RB and DPS-1200FB. They have high power density and are usually inexpensive, making them useful as lab 12V high-current supplies, charger front ends, 3D printer / CNC / radio equipment power supplies, or custom server PSU backplanes.

Note that Common Slot is more of a common slot form factor within a server vendor ecosystem. It is not the same kind of broadly published consumer standard as ATX. Different models are often very similar, but before building a breakout board or applying power directly, it is still best to compare the specific PSU model documentation and actual measurements.

Interface Structure

Common CSPS power supplies use a 64 pin edge connector for output. Based on Jayy’s open-source breakout board project, the connector can be a 2.54mm pitch 64 pin edge connector, for example:

Vertical: WingTat S-64M-2.54-5
Right angle: WingTat S-64L-2.54-5

The high-current section is not carried by a single pin. Instead, multiple 12V and GND pins are paralleled. This reduces current per contact, lowers heating caused by contact resistance, and makes current sharing on the backplane easier.

The signal section is concentrated in the middle pins and includes:

EN: main output enable control.
PRE: power supply present detection.
12VSB: standby 12V, usually always on when AC input is present, with limited current capability.
SCL / SDA: PMBus / SMBus / I2C communication.
PSOK: power supply OK signal.
IMON: current monitor signal.
PSIN: alarm / status related signal.
ADR: PMBus address related pin.

64 Pin Pinout

The following table follows common HP / HPE Common Slot, DPS-750RB, and DPS-1200FB community documentation. Be careful: this is a double-sided card edge, not a single row of pins 1-64. In Slundell’s DPS-1200FB notes, the bottom side has pins 1-32 and the top side has pins 33-64. When designing a breakout board, also confirm the left/right orientation and the physical alignment between the two sides.

Side	Pin	Signal	Description
Bottom	01-13	`12V`	Main power `+12V` output
Bottom	14-26	`GND`	Main power ground / return
Bottom	27	`ADR`	PMBus address setting / address related signal
Bottom	28	`NC`	Not connected
Bottom	29	`NC`	Not connected
Bottom	30	`GND`	Signal ground for control and PMBus reference
Bottom	31	`SCL`	PMBus / SMBus / I2C clock; some compatible documentation may swap this label with Pin 32
Bottom	32	`SDA`	PMBus / SMBus / I2C data; some compatible documentation may swap this label with Pin 31
Top	33	`EN` / `PSON#`	Active-low enable pin; pull to signal ground to enable the main 12V output
Top	34	`IMON` / `LOAD_SHARE`	Current monitor or load-share related analog signal, depending on documentation
Top	35	`PSOK` / `STATUS`	Power OK / power supply normal status
Top	36	`PRE` / `PRESENT#`	Present detect pin, often the short pin; pull high as part of enabling the main output
Top	37	`12VSB`	12V standby power, low current, usually always on
Top	38	`PSIN` / `PSALARM` / `PSINTERRUPT`	Power supply alarm / interrupt / status signal
Top	39-51	`GND`	Main power ground / return
Top	52-64	`12V`	Main power `+12V` output

In the physical alignment, bottom-side pins 1-13 and top-side pins 52-64 occupy the same section, and both are high-current 12V. Bottom-side pins 14-26 and top-side pins 39-51 occupy the same section, and both are GND. The control and management signals are concentrated at the same physical end on pins 27-38. When designing a PCB, 12V and GND should use large copper pours, many parallel vias, sufficiently wide traces, or copper bars. Signal lines should stay away from high-current switching loops to avoid coupling current ripple and contact noise into the management interface.

Different references do not always use the same names for every signal. For example, Pin 34 may be called IMON, I Monitor, or LOAD_SHARE, and Pin 38 may be called PSIN, PSALARM, or PSINTERRUPT. Murata D1U86P-type compatible supply documentation may also label Pin 31 / Pin 32 SDA and SCL in the opposite order from HP DPS community notes. Before connecting PMBus, verify against the exact PSU datasheet, the original backplane schematic, or your own measurements.

Enabling the 12V Main Output

After AC power is applied, a CSPS power supply usually does not immediately enable the high-current 12V main output. To turn on the main output, the PRE and EN signals need to be handled.

Proper Enable Method

Pull PRE, Pin 36, up to 12VSB, Pin 37.
Pull EN, Pin 33, down to signal ground. Pin 30 is recommended.

In practical terms:

PRE tells the power supply that the module has been inserted into the backplane and the system allows it to enter the working state.
EN is an active-low enable signal. Pulling it low turns on the main 12V output.
12VSB can power a control board, MCU, fan controller, or soft-start circuit, but it should not be used as a high-current output.

If using an MCU for control, a safer approach is:

Power the MCU from 12VSB through a DC-DC converter or LDO.
Pull EN down to signal ground through an open-drain output, N-MOS, or optocoupler.
Pull PRE up to 12VSB through a suitable resistor.
After power-on, check status first, then enable EN after a delay.

Quick Test Method

According to the open-source breakout board project, you can also place a resistor between Pin 33 EN and Pin 36 PRE to enable the output. Many people short the pins directly, but using a resistor is recommended instead of a hard short.

This method is suitable for temporary testing, not for a finished power supply intended for long-term operation. For long-term use, it is better to handle the signals as PRE -> 12VSB and EN -> GND, and leave protection and test points for the control signals.

PMBus / SMBus / I2C Management Interface

Pin 31 SCL and Pin 32 SDA are the management bus. Many server power supplies support PMBus internally and can expose or configure status information such as:

Output voltage, current, and power.
Temperature and fan status.
Input voltage status.
Alarm, fault, and protection states.
Manufacturer, model, serial number, and other identification data.

Several details are worth noting:

PMBus is based on SMBus / I2C, but its command set is not the same as an ordinary I2C sensor.
Different power supplies expose different commands. Some commands are read-only, and some may be vendor locked.
ADR may affect the device address, which is useful for multi-PSU parallel or redundant backplanes.
Before connecting an MCU or USB-I2C tool, confirm the bus voltage level. Do not assume it can be connected directly to 5V.
SCL / SDA usually need pull-up resistors. The pull-up voltage and resistance should be decided based on the PSU documentation and measurements.

If you only want to use the PSU as a high-power 12V output, you can leave PMBus disconnected at first and only handle PRE, EN, 12VSB, and GND. If you want to build a full monitoring panel or automatic protection, PMBus becomes very useful.

Breakout Board Design Notes

High-Current Output

Common CSPS power supplies range from several hundred watts to more than one kilowatt. At 12V output:

750W is about 62.5A.
1200W is about 100A.

This is far beyond what ordinary Dupont wires, breadboards, or thin PCB traces can safely carry. When designing a breakout board:

Use large copper pours or copper bars for 12V and GND.
Choose output terminals with sufficient current rating, such as Anderson Powerpole, copper studs, terminal blocks, or XT series high-current connectors.
Connect multiple 12V pins and multiple GND pins. Using only a few contacts can cause overheating.
Add fuses, circuit breakers, or electronic protection to the output.
During long high-current operation, check the temperature rise of connectors, solder joints, and cables.

Control Signals

Control signals should not share long thin return paths with the main current. Recommended practices:

Bring out Pin 30 signal ground separately as the reference ground for the MCU / control board.
Pull EN down with a transistor or MOSFET. Do not let the MCU directly take unknown transients.
Add current limiting, voltage division, or protection before feeding PSOK, PSIN, and IMON into an MCU.
Keep PMBus traces short and place a ground reference nearby.

Cooling and Noise

Server power supplies are designed for rack servers and usually rely on high airflow. When used standalone, common issues include:

Fans can still be noisy at no load or light load.
Connectors and output terminals heat up under high current.
Some models may need a minimum load to stay stable.
Parallel operation requires additional care for current sharing and reverse current.

For a lab supply, place it in a well-ventilated area and add a voltmeter, ammeter, and temperature monitoring at the output. Do not seal it in a small box with no airflow for long-term full-load operation.

Common CSPS Power Supply Models

When searching for CSPS power supplies on the used market, three sets of numbers are often mixed together:

Option Part Number: HPE option number, commonly in the form 503296-B21.
Spare Part Number / SPS: spare part number, commonly in the form 511777-001.
PSU body model: commonly in the form DPS-750RB A, HSTNS-PL18, or PS-2751-7CB-LF.

Do not look at only one number when buying a PSU. It is better to check the power rating, input voltage range, edge connector form, and label model at the same time. The following are common Common Slot / CSPS related models for initial filtering.

HPE Common Slot Option Numbers

Power	Common HPE option number	Common spare / generic numbers	Notes
460W	`503296-B21`	`499249-001`, `511777-001`	460W AC Common Slot Gold Hot Plug
460W	`656362-B21`	`643931-001`, `643954-201`, `660184-001`	460W Common Slot Platinum series
750W	`512327-B21`	`506821-001`, `506822-201`, `511778-001`	750W Common Slot series, common `DPS-750RB`
750W	`593831-B21`	`591556-101`, `591554-001`, `599383-001`	750W Common Slot series
750W	`656363-B21`	`643932-001`, `643955-101`, `660183-001`	750W Common Slot Platinum series
750W	`739254-B21`	`746072-001`, `748281-201`, `742516-001`	750W Common Slot series
750W	`697581-B21`	`697579-001`, `700287-001`, `697554-201`	750W Common Slot Platinum series
1200W	`438202-001` / `438202-002`	`440785-001`	1200W Common Slot series, common `DPS-1200FB`
1200W	`656364-B21`	`643933-001`, `643956-101`, `660185-001`, `643956-201`	1200W Common Slot Platinum series
1500W	`684532-B21`	`684529-001`, `684530-201`, `704604-001`	1500W Common Slot Platinum Plus series

Common Models Seen on PSU Labels

Power range	Common PSU model / code	Common HPE numbers
460W	`DPS-460EB A`, `HSTNS-PD14`, `HSTNS-PL14`	`499249-001`, `499250-101`, `499250-201`, `511777-001`, `503296-B21`
460W	`HSTNS-PL23B`, `PS-2461-6C1-LF`	`591553-001`, `591555-201`, `599381-001`
460W	`DPS-460MB A`, `HSTNS-PL28`, `PS-2461-7C-LF`	`643931-001`, `643954-201`, `660184-001`, `656362-B21`
460W	`HSTNS-PR28-AD`, `HSTNS-PL28-AD`, `7001613-J100`	`746071-001`, `748279-201`, `748279-301`, `742515-001`, `739252-B21`
750W	`DPS-750RB-A`, `HSTNS-PL18`, `HSTNS-PD18`	`506821-001`, `506822-101`, `506822-201`, `511778-001`, `512327-B21`
750W	`HSTNS-PL12`	`449838-001`, `449840-001`, `454353-001`
750W	`DPS-750AB-4 A`, `HSTNS-PD31`	`674890-001`, `666375-101`, `674275-B21`
750W	`DPS-750UB B`, `HSTNS-PD22B`	`591556-101`, `591554-001`, `599383-001`, `593831-B21`
750W	`DPS-750AB-3 A`, `HSTNS-PD29`	`643932-001`, `643955-101`, `660183-001`, `656363-B21`
750W	`HSTNS-PL29-AD`, `PS-2751-7CB-LF`	`746072-001`, `748281-201`, `742516-001`, `739254-B21`
750W	`HSTNS-PL34`, `PS-2751-9C-LF`	`697579-001`, `700287-001`, `697554-201`, `697581-B21`
1200W	`DPS-1200FB A`, `HSTNS-PD11`	`440785-001`, `438202-001`, `438202-002`
1200W	`DPS-1200FB-1 A`, `HSTNS-PD19`	`570451-001`, `570451-101`, `579229-001`
1200W	`DPS-1200SB A`, `HSTNS-PD30`	`643933-001`, `643956-101`, `660185-001`, `643956-201`, `656364-B21`
1200W	`DPS-1200LB C`	`MVKTR-LF`
1500W	`HSTNS-PL33`, `PS-2152-1C-LF`	`684529-001`, `684530-201`, `704604-001`, `684532-B21`
2400W	`DPS-2400AB`	Verify against the specific label

Do Not Confuse It With Flex Slot

HPE later introduced Flex Slot power supplies, such as 500W / 800W / 1400W / 1600W / 1800W-2200W series. Flex Slot is also a hot-plug server PSU form factor, but it is smaller than the previous Common Slot generation, and the connector and breakout board are usually not directly compatible. This article mainly covers the 64 pin edge connector Common Slot / CSPS type. Do not assume that any hot-plug server PSU can use the same breakout board.

Some Huawei server power supplies have an appearance and connector that are very close to HP Common Slot, but not all Huawei hot-plug 12V power supplies should be classified as CSPS. Many previously mentioned PAC*, PDC*, EPW*, PHD*, and TPS* models are simply server hot-plug PSU series. Their connector size, control pins, and startup logic may not match HP 64 pin Common Slot.

At present, the following model can be listed more confidently as Huawei-related CSPS / Common Slot form factor:

Model	Manufacturer	Huawei part number / related marking	Common systems	Specification	Notes
`PS-2122-3H`	Lite-On	`02130985`, `WEPW12K00`, sometimes written as `PS-2L22-3H`	Often seen in used Huawei X6000, RH1288 V2/V3, RH2288 V2/V3 parts	1200W, `+12V 100A`, `+12VSB 2.5A`	Documentation and used-parts listings both point to a 1200W 12V hot-plug module used in Huawei servers, with an appearance close to Common Slot PSUs

The output capability of PS-2122-3H depends on the input voltage range. Common markings are:

100V input: +12V 62.5A, about 750W.
110-127V input: +12V 75A, about 900W.
200-240V AC or 240V DC input: +12V 100A, about 1200W.
Standby output: +12VSB 2.5A.

Huawei EPW750-12A type 750W power supplies are often compared with HP DPS-750RB A. They also have an edge connector, 12V main output, and 12VSB, and there is a user report that HP DPS-750RB A worked in a Huawei RH2288H V3. However, this is more like a clue from physical appearance and partial compatibility testing, and it is not enough to put EPW750-12A into the confirmed CSPS model table. A safer description is: treat it as a model to be verified, and confirm the edge connector pinout, enable logic, and PMBus behavior before use.

The following Huawei power supplies should not currently be written directly as CSPS-compatible models:

PAC550S12-BE
PAC900S12-BE
PAC1500S12-BE
PAC2000S12-BE
PAC2000S12-TE
EPW3000-12A
PHD3000S12-CE
TPS2500-12D
PDC1200S12-CE

They are all common Huawei server / telecom equipment 12V hot-plug power supplies, but “hot-plug 12V power supply” does not mean “HP Common Slot / CSPS pinout compatible.” If clear edge connector photos, original pinout tables, or measured pinouts are found later, they can be added to the confirmed table separately.

In theory, Common Slot power supplies with the same 64 pin edge connector and the same pinout may be compatible. However, used power supplies can come from many sources and may have vendor-specific firmware, different power ratings, different fan policies, or different management commands. Before actual use, it is best to verify with low risk:

Apply only AC input with no load, and confirm whether 12VSB is normal.
Handle PRE / EN with a resistor method, and confirm whether the main 12V starts.
Add a small load and test voltage stability.
Increase the load gradually while observing temperature rise, fan behavior, and protection behavior.

Summary

The core idea of CSPS / Common Slot server power supplies is straightforward:

Many pins at both ends are paralleled for 12V and GND.
A small number of middle pins handle enable, status, standby power, and PMBus management.
The main output requires PRE and EN to work together before it turns on.
12VSB is standby power for control circuitry, not the main output.
The real difficulty is not “turning it on,” but high-current connection, cooling, protection, and long-term reliability.

For a simple breakout board, at minimum you need to connect 12V, GND, 12VSB, PRE, and EN. For a complete backplane, SCL, SDA, ADR, PSOK, IMON, and PSIN should also be brought out for later monitoring and automatic control.

References

Common CSPS Power Supply Models

When searching for CSPS power supplies on the used market, three sets of numbers are often mixed together:

Option Part Number: HPE option number, commonly in the form 503296-B21.
Spare Part Number / SPS: spare part number, commonly in the form 511777-001.
PSU body model: commonly in the form DPS-750RB A, HSTNS-PL18, or PS-2751-7CB-LF.

HPE Common Slot Option Numbers

Power	Common HPE option number	Common spare / generic numbers	Notes
460W	`503296-B21`	`499249-001`, `511777-001`	460W AC Common Slot Gold Hot Plug
460W	`656362-B21`	`643931-001`, `643954-201`, `660184-001`	460W Common Slot Platinum series
750W	`512327-B21`	`506821-001`, `506822-201`, `511778-001`	750W Common Slot series, common `DPS-750RB`
750W	`593831-B21`	`591556-101`, `591554-001`, `599383-001`	750W Common Slot series
750W	`656363-B21`	`643932-001`, `643955-101`, `660183-001`	750W Common Slot Platinum series
750W	`739254-B21`	`746072-001`, `748281-201`, `742516-001`	750W Common Slot series
750W	`697581-B21`	`697579-001`, `700287-001`, `697554-201`	750W Common Slot Platinum series
1200W	`438202-001` / `438202-002`	`440785-001`	1200W Common Slot series, common `DPS-1200FB`
1200W	`656364-B21`	`643933-001`, `643956-101`, `660185-001`, `643956-201`	1200W Common Slot Platinum series
1500W	`684532-B21`	`684529-001`, `684530-201`, `704604-001`	1500W Common Slot Platinum Plus series

Common Models Seen on PSU Labels

Power range	Common PSU model / code	Common HPE numbers
460W	`DPS-460EB A`, `HSTNS-PD14`, `HSTNS-PL14`	`499249-001`, `499250-101`, `499250-201`, `511777-001`, `503296-B21`
460W	`HSTNS-PL23B`, `PS-2461-6C1-LF`	`591553-001`, `591555-201`, `599381-001`
460W	`DPS-460MB A`, `HSTNS-PL28`, `PS-2461-7C-LF`	`643931-001`, `643954-201`, `660184-001`, `656362-B21`
460W	`HSTNS-PR28-AD`, `HSTNS-PL28-AD`, `7001613-J100`	`746071-001`, `748279-201`, `748279-301`, `742515-001`, `739252-B21`
750W	`DPS-750RB-A`, `HSTNS-PL18`, `HSTNS-PD18`	`506821-001`, `506822-101`, `506822-201`, `511778-001`, `512327-B21`
750W	`HSTNS-PL12`	`449838-001`, `449840-001`, `454353-001`
750W	`DPS-750AB-4 A`, `HSTNS-PD31`	`674890-001`, `666375-101`, `674275-B21`
750W	`DPS-750UB B`, `HSTNS-PD22B`	`591556-101`, `591554-001`, `599383-001`, `593831-B21`
750W	`DPS-750AB-3 A`, `HSTNS-PD29`	`643932-001`, `643955-101`, `660183-001`, `656363-B21`
750W	`HSTNS-PL29-AD`, `PS-2751-7CB-LF`	`746072-001`, `748281-201`, `742516-001`, `739254-B21`
750W	`HSTNS-PL34`, `PS-2751-9C-LF`	`697579-001`, `700287-001`, `697554-201`, `697581-B21`
1200W	`DPS-1200FB A`, `HSTNS-PD11`	`440785-001`, `438202-001`, `438202-002`
1200W	`DPS-1200FB-1 A`, `HSTNS-PD19`	`570451-001`, `570451-101`, `579229-001`
1200W	`DPS-1200SB A`, `HSTNS-PD30`	`643933-001`, `643956-101`, `660185-001`, `643956-201`, `656364-B21`
1200W	`DPS-1200LB C`	`MVKTR-LF`
1500W	`HSTNS-PL33`, `PS-2152-1C-LF`	`684529-001`, `684530-201`, `704604-001`, `684532-B21`
2400W	`DPS-2400AB`	Verify against the specific label

Do Not Confuse It With Flex Slot

At present, the following model can be listed more confidently as Huawei-related CSPS / Common Slot form factor:

Model	Manufacturer	Huawei part number / related marking	Common systems	Specification	Notes
`PS-2122-3H`	Lite-On	`02130985`, `WEPW12K00`, sometimes written as `PS-2L22-3H`	Often seen in used Huawei X6000, RH1288 V2/V3, RH2288 V2/V3 parts	1200W, `+12V 100A`, `+12VSB 2.5A`	Documentation and used-parts listings both point to a 1200W 12V hot-plug module used in Huawei servers, with an appearance close to Common Slot PSUs

The output capability of PS-2122-3H depends on the input voltage range. Common markings are:

100V input: +12V 62.5A, about 750W.
110-127V input: +12V 75A, about 900W.
200-240V AC or 240V DC input: +12V 100A, about 1200W.
Standby output: +12VSB 2.5A.

The following Huawei power supplies should not currently be written directly as CSPS-compatible models:

PAC550S12-BE
PAC900S12-BE
PAC1500S12-BE
PAC2000S12-BE
PAC2000S12-TE
EPW3000-12A
PHD3000S12-CE
TPS2500-12D
PDC1200S12-CE

Apply only AC input with no load, and confirm whether 12VSB is normal.
Handle PRE / EN with a resistor method, and confirm whether the main 12V starts.
Add a small load and test voltage stability.
Increase the load gradually while observing temperature rise, fan behavior, and protection behavior.

Summary

The core idea of CSPS / Common Slot server power supplies is straightforward:

Many pins at both ends are paralleled for 12V and GND.
A small number of middle pins handle enable, status, standby power, and PMBus management.
The main output requires PRE and EN to work together before it turns on.
12VSB is standby power for control circuitry, not the main output.
The real difficulty is not “turning it on,” but high-current connection, cooling, protection, and long-term reliability.

References

M.2 Key E, Key B, and Key M Pinout Notes

Wed, 15 Apr 2026 08:00:00 +0800

This article mainly covers three M.2 interfaces that are very common in embedded systems:

Socket 1 - Key E
Socket 2 - Key B
Socket 3 - Key M

The original document is based on PCI Express M.2 Specification Revision 3.0, Version 1.2.

01 Socket 1 - Key E

Key E is commonly used for connectivity modules such as Wi-Fi / Bluetooth expansion cards. The original text notes that these cards usually connect over PCIe and USB, while support for other buses such as SDIO and I2S depends on whether the COM supports them.

Pinout Description

Left Pin	Left Signal	Right Signal	Right Pin
74	3.3V	GND	75
72	3.3V	RESERVED/REFCLKn1	73
70	UIM_POWER_SRC/GPIO_1/PEWAKE1#	RESERVED/REFCLKp1	71
68	UIM_POWER_SNK/CLKREQ1#	GND	69
66	UIM_SWP/PERST1#	RESERVED/PERn1	67
64	RESERVED	RESERVED/PERp1	65
62	ALERT# (I)(0/1.8 V)	GND	63
60	I2C_CLK (O)(0/1.8 V)	RESERVED/PETn1	61
58	I2C_DATA (I/O)(0/1.8 V)	RESERVED/PETp1	59
56	W_DISABLE1# (O)(0/3.3V)	GND	57
54	W_DISABLE2# (O)(0/3.3V)	PEWAKE0# (I/O)(0/3.3V)	55
52	PERST0# (O)(0/3.3V)	CLKREQ0# (I/O)(0/3.3V)	53
50	SUSCLK(32kHz) (O)(0/3.3V)	GND	51
48	COEX_TXD (O)(0/1.8V)	REFCLKn0	49
46	COEX_RXD (I)(0/1.8V)	REFCLKp0	47
44	COEX3 (I/O)(0/1.8V)	GND	45
42	VENDOR DEFINED	PERn0	43
40	VENDOR DEFINED	PERp0	41
38	VENDOR DEFINED	GND	39
36	UART RTS (O)(0/1.8V)	PETn0	37
34	UART CTS (I)(0/1.8V)	PETp0	35
32	UART TXD (O)(0/1.8V)	GND	33
Key E	Key E
Key E	Key E
Key E	Key E
Key E	SDIO RESET#/TX_BLANKING (O)(0/1.8V)	23
22	UART RXD (I)(0/1.8V)	SDIO WAKE# (I)(0/1.8V)	21
20	UART WAKE# (I)(0/3.3V)	SDIO DATA3(I/O)(0/1.8V)	19
18	GND	SDIO DATA2(I/O)(0/1.8V)	17
16	LED_2# (I)(OD)	SDIO DATA1(I/O)(0/1.8V)	15
14	PCM_OUT/I2S SD_OUT (O)(0/1.8V)	SDIO DATA0(I/O)(0/1.8V)	13
12	PCM_IN/I2S SD_IN (I)(0/1.8V)	SDIO CMD(I/O)(0/1.8V)	11
10	PCM_SYNC/I2S WS (I/O)(0/1.8V)	SDIO CLK/SYSCLK (O)(0/1.8V)	9
8	PCM_CLK/I2S SCK (I/O)(0/1.8V)	GND	7
6	LED_1# (I)(OD)	USB_D-	5
4	3.3V	USB_D+	3
2	3.3V	GND	1

Notes

M.2 Socket 1 - Key E is commonly used for connectivity applications such as Wi-Fi / Bluetooth modules.
The AC coupling capacitors for PCIe_TX+/- are placed on the COM side, while the AC coupling capacitors for PCIe_RX+/- are placed on the M.2 add-in card side, so the carrier board does not need to add those AC coupling capacitors again.
CLKREQ# is used to enable the PCIe reference clock and should be connected to the output enable pin of the PCIe clock buffer.
Since CLKREQ# is an active-low open-drain signal driven by the M.2 add-in card, the carrier board side needs a pull-up resistor.

02 Socket 2 - Key B

Key B is common on SATA and PCIe SSDs, as well as some WWAN modules. One key feature of this socket is the set of four configuration pins, CONFIG_0 through CONFIG_3, which let the system identify which host interface the card expects to use.

Pinout Description

Left Pin	Left Signal	Right Signal	Right Pin
74	3.3 V/VBAT	CONFIG_2	75
72	3.3 V/VBAT	GND	73
70	3.3 V/VBAT	GND	71
68	SUSCLK(32kHz) (O)(0/3.3V)	CONFIG_1	69
66	SIM DETECT (O)	RESET# (O)(0/1.8V)	67
64	COEX_RXD (I)(0/1.8V)	ANTCTL3 (I)(0/1.8V)	65
62	COEX_TXD (O)(0/1.8V)	ANTCTL2 (I)(0/1.8V)	63
60	COEX3 (I/O)(0/1.8V)	ANTCTL1 (I)(0/1.8V)	61
58	NC	ANTCTL0 (I)(0/1.8V)	59
56	NC	GND	57
54	PEWAKE# (I/O)(0/3.3V)	REFCLKp	55
52	CLKREQ# (I/O)(0/3.3V)	REFCLKn	53
50	PERST# (O)(0/3.3V)	GND	51
48	GPIO_4 (I/O)(0/1.8V)	PETp0/SATA-A+	49
46	GPIO_3 (I/O)(0/1.8V)	PETn0/SATA-A-	47
44	GPIO_2 (I/O)/ALERT# (I)/(0/1.8V)	GND	45
42	GPIO_1 (I/O)/SMB_DATA (I/O)/(0/1.8V)	PERp0/SATA-B-	43
40	GPIO_0 (I/O)/SMB_CLK (I/O)/(0/1.8V)	PERn0/SATA-B+	41
38	DEVSLP (O)	GND	39
36	UIM-PWR (I)	PETp1/USB3.1-Tx+/SSIC-TxP	37
34	UIM-DATA (I/O)	PETn1/USB3.1-Tx-/SSIC-TxN	35
32	UIM-CLK (I)	GND	33
30	UIM-RESET (I)	PERp1/USB3.1-Rx+/SSIC-RxP	31
28	GPIO_8 (I/O) (0/1.8V)	PERn1/USB3.1-Rx-/SSIC-RxN	29
26	GPIO_10 (I/O) (0/1.8V)	GND	27
24	GPIO_7 (I/O) (0/1.8V)	DPR (O) (0/1.8V)	25
22	GPIO_6 (I/O)(0/1.8V)	GPIO_11 (I/O) (0/1.8V)	23
20	GPIO_5 (I/O)(0/1.8V)	CONFIG_0	21
Key B	Key B
Key B	Key B
Key B	Key B
Key B	GND	11
10	GPIO_9/DAS/DSS (I/O)/LED_1# (I)(0/3.3V)	USB_D-	9
8	W_DISABLE1# (O)(0/3.3V)	USB_D+	7
6	FULL_CARD_POWER_OFF# (O)(0/1.8V or 3.3V)	GND	5
4	3.3 V	GND	3
2	3.3 V	CONFIG_3	1

Host Interface Configuration

The original text explains that the system should read the four CONFIG_X pins to determine the selected pinout / host interface for the installed card. Even when the M.2 card is not powered yet, the system should still pull these configuration pins up to the appropriate rail so their state can be read.

CONFIG_0 (Pin 21)	CONFIG_1 (Pin 69)	CONFIG_2 (Pin 75)	CONFIG_3 (Pin 1)	Host Interface
0	0	0	0	SSD - SATA
0	1	0	0	SSD - PCIe
0	0	1	0	WWAN - PCIe (Port Configuration 0*)
0	1	1	0	WWAN - PCIe (Port Configuration 1*)
0	0	0	1	WWAN - PCIe, USB3.1 Gen1 (Port Configuration 0*)
0	1	0	1	WWAN - PCIe, USB3.1 Gen1 (Port Configuration 1*)
0	0	1	1	WWAN - PCIe, USB3.1 Gen1 (Port Configuration 2*)
0	1	1	1	WWAN - PCIe, USB3.1 Gen1 (Port Configuration 3*)
1	0	0	0	WWAN - SSIC (Port Configuration 0*)
1	1	0	0	WWAN - SSIC (Port Configuration 1*)
1	0	1	0	WWAN - SSIC (Port Configuration 2*)
1	1	1	0	WWAN - SSIC (Port Configuration 3*)
1	0	0	1	WWAN - PCIe (Port Configuration 2*)
1	1	0	1	WWAN - PCIe (Port Configuration 3*)
1	0	1	1	WWAN - PCIe, USB3.1 Gen1 (vendor defined)
1	1	1	1	No Add-in Card Present

Note: for the details of each Port Configuration, the original text suggests referring back to the PCI Express M.2 Specification.

Notes

Socket 2 - Key B is commonly used for PCIe or SATA storage devices.
CONFIG_1 can be used to switch the host interface:
CONFIG_1 = Low enables SATA
CONFIG_1 = High enables PCIe
The second PCIe lane can support PCIe x2 devices such as Intel Optane. To actually run at x2, the host PCIe lanes must also be configured as a PCIe x2 link.
When PCIe mode is enabled, the M.2 add-in card does not connect CONFIG_1, so the carrier board side needs a pull-up resistor.
If this M.2 socket is used with a SATA storage device, Pin 43 should connect to the negative side of the SATA Rx differential pair.
If this M.2 socket is used with a PCIe storage device, Pin 43 should connect to the positive side of the PCIe Rx differential pair.

03 Socket 3 - Key M

Key M is commonly used for PCIe or SATA storage devices, especially higher-bandwidth SSDs. Similar to Key B, it also has a signal used to select the host interface, but here that signal is PEDET.

Pinout Description

Left Pin	Left Signal	Right Signal	Right Pin
74	3.3 V	GND	75
72	3.3 V	GND	73
70	3.3 V	GND	71
68	SUSCLK (O)(0/3.3V)	PEDET	69
Key M	NC	67
Key M	Key M
Key M	Key M
Key M	Key M
Key M	Key M
58	NC	GND	57
56	NC	REFCLKp	55
54	PEWAKE# (I/O)(0/3.3V) or NC	REFCLKn	53
52	CLKREQ# (I/O)(0/3.3V) or NC	GND	51
50	PERST# (O)(0/3.3V) or NC	PETp0/SATA-A+	49
48	NC	PETn0/SATA-A-	47
46	NC	GND	45
44	ALERT# (I) (0/1.8V)	PERp0/SATA-B-	43
42	SMB_DATA (I/O) (0/1.8V)	PERn0/SATA-B+	41
40	SMB_CLK (I/O)(0/1.8V)	GND	39
38	DEVSLP (O)	PETp1	37
36	NC	PETn1	35
34	NC	GND	33
32	NC	PERp1	31
30	NC	PERn1	29
28	NC	GND	27
26	NC	PETp2	25
24	NC	PETn2	23
22	NC	GND	21
20	NC	PERp2	19
18	3.3 V	PERn2	17
16	3.3 V	GND	15
14	3.3 V	PETp3	13
12	3.3 V	PETn3	11
10	DAS/DSS (I/O)/LED_1# (I)(0/3.3V)	GND	9
8	NC	PERp3	7
6	NC	PERn3	5
4	3.3 V	GND	3
2	3.3 V	GND	1

Notes

Socket 3 - Key M is commonly used for PCIe or SATA storage devices.
PEDET is used to select the host interface, and the M.2 card indicates the mode by how it is wired:
PEDET = Low means SATA is enabled, which is done by connecting PEDET to GND on the M.2 card
PEDET = High means PCIe is enabled, which is done by leaving PEDET unconnected on the M.2 card
For maximum bandwidth, all four PCIe lanes should be configured as an x4 link.
When PCIe mode is enabled, the M.2 add-in card does not connect PEDET, so the carrier board side needs a pull-up resistor.
If this socket is used with a SATA storage device, Pin 43 should connect to the negative side of the SATA Rx differential pair.
If this socket is used with a PCIe storage device, Pin 43 should connect to the positive side of the PCIe Rx differential pair.

04 Quick Summary

If you only want the quickest takeaways from this article, these are the main points:

Key E is mainly aimed at connectivity modules such as Wi-Fi / Bluetooth.
Key B is common on SATA / PCIe SSDs and can also appear on WWAN modules.
Key M is mainly used for higher-bandwidth storage, especially PCIe SSDs.
Key B uses CONFIG_0 ~ CONFIG_3 to identify the interface configuration.
Key M uses PEDET to distinguish between SATA and PCIe.
Signals such as CLKREQ#, CONFIG_1, and PEDET need pull-ups on the carrier board in some modes.

If you plan to design a carrier board or a socket interface around these definitions, it is still a good idea to compare this summary with the original source and the PCI Express M.2 specification, especially for Port Configuration, PCIe lane mapping, and pins shared between SATA and PCIe.

References

Source material: https://wiki.congatec.com/wiki/M.2_Pinout_Descriptions_and_Reference_Designs_(AN43)

Intel ATX12VO Power Connector Pinout

Thu, 26 May 2022 00:00:00 +0000

ATX12VO is Intel’s 12V-only desktop power supply design. Compared with traditional ATX power supplies, it removes most 3.3V and 5V rails from the PSU side and mainly provides 12V to the motherboard.

The motherboard then performs local conversion for 5V, 3.3V and other lower-voltage rails.

Why ATX12VO Exists

The goal of ATX12VO is to improve standby efficiency and simplify the power supply output structure.

Traditional ATX power supplies provide multiple rails, including 12V, 5V and 3.3V. But modern PCs consume most power from 12V. Keeping several low-voltage rails active inside the PSU can reduce efficiency, especially at low load.

ATX12VO moves more conversion work to the motherboard.

Connector Difference

Traditional ATX motherboards usually use a 24-pin main power connector.

ATX12VO uses a smaller main connector because it mainly carries 12V and control signals. It does not provide the same set of 3.3V and 5V pins as a standard ATX 24-pin connector.

This means ATX12VO power supplies and motherboards are not directly interchangeable with standard ATX hardware unless the platform explicitly supports it.

Practical Notes

When checking an ATX12VO system, pay attention to:

motherboard compatibility;
PSU connector type;
SATA power support;
5V and 3.3V conversion on the motherboard;
standby power behavior;
OEM-specific wiring changes.

Do not plug cables based only on connector shape. Always confirm the pinout and platform documentation.

Summary

ATX12VO is a 12V-centered power design. It can improve efficiency and simplify PSU output, but it also changes power distribution responsibilities. Compatibility must be checked at the motherboard and PSU level before reuse or modification.

PCI-E 6-Pin and 6+2-Pin GPU Power Connector Pinout

Thu, 26 May 2022 00:00:00 +0000

Modern discrete graphics cards usually cannot rely only on the PCI-E slot for power. Higher-end GPUs need extra power from PCI-E auxiliary connectors, most commonly 6-pin and 6+2-pin connectors.

Why Extra Power Is Needed

The PCI-E slot itself can provide limited power. When a GPU needs more power than the slot can safely provide, the graphics card uses external PCI-E power connectors from the power supply.

The common connector types are:

PCI-E 6-pin;
PCI-E 6+2-pin, which can be used as either 6-pin or 8-pin.

6-Pin And 6+2-Pin

A 6+2-pin connector is essentially an 8-pin connector split into 6 pins plus 2 additional pins. The split design improves compatibility, allowing the same cable to work with cards that need either 6-pin or 8-pin input.

The difference is not about performance by itself. It is mainly about compatibility and power capacity.

Power Capacity

PCI-E auxiliary connectors mainly provide 12V power.

In physical wiring terms, a 6-pin connector has fewer 12V and ground lines than an 8-pin connector. A 6+2-pin or 8-pin connector can carry more current.

However, connector physical capacity and PCI-E specification limits are not the same thing. In the PCI-E specification, a 6-pin connector is usually rated for up to 75W, while an 8-pin connector is usually rated for up to 150W.

Practical Advice

When connecting GPU power:

use dedicated PCI-E power cables from the PSU;
avoid mixing modular PSU cables from different brands;
do not overload one cable with too many adapters;
check the GPU vendor’s recommended PSU wattage;
make sure the connector is fully inserted.

Loose or overloaded GPU power connectors can cause crashes, overheating or connector damage.

Summary

PCI-E 6-pin and 6+2-pin connectors provide additional 12V power for graphics cards. The 6+2-pin design improves compatibility with both 6-pin and 8-pin GPU sockets. Always follow the GPU and PSU documentation when wiring high-power graphics cards.

ATX Power Connector Pinouts

Thu, 24 Mar 2022 00:00:00 +0000

ATX 20-pin pinout

ATX 24-pin pinout

CPU 4-pin pinout

4D connector pinout

GPU 6-pin pinout (6-pin PCI Express)

GPU 6+2-pin pinout (8-pin PCI Express)

SATA power pinout

ATX full diagram

Wire color references

Red: +5V, logic rails and some device power
Yellow: +12V, CPU/GPU and major power rails
Orange: +3.3V, common motherboard/device rails
Purple: +5VSB, standby rail (USB wake, standby features)
Black: GND (0V)
Green: PS_ON (short to GND to start PSU)
Gray: Power Good (PWR_OK)

Pinout on KnightLi Blog

TerraMaster F2-221 NAS Backplane Pinout Notes

Summary

Backplane Connector Pinout

Signal Source Reasoning

PCIe Differential Pair Identification

Validation

Notes

Related Links

CRPS Common Redundant Server Power Supply Standard, Pin Functions, and Common Models

CRPS vs CSPS

Standard 2x25 Edge Connector Pinout

Pin Function Notes

High-Current Output

+12VSB

PSON#

PWOK

PMBus_SDA / PMBus_SCL

A0 / A1

SMBAlert#

SMART_ON / CR_BUS#

+12V Remote Sense / +12V Return Sense

+12V Share Bus#

PRESENT#

VIN_GOOD / PS_KILL / NC

Basic Approach to Starting a CRPS PSU

Breakout Board Design Notes

Common CRPS / M-CRPS Models and Series

How to Judge Compatibility Before Buying or Reusing

Summary

References

CSPS Common Slot Server Power Supply Interface and Pinout

Interface Structure

64 Pin Pinout

Enabling the 12V Main Output

Proper Enable Method

Quick Test Method

PMBus / SMBus / I2C Management Interface

Breakout Board Design Notes

High-Current Output

Control Signals

Cooling and Noise

Common CSPS Power Supply Models

HPE Common Slot Option Numbers

Common Models Seen on PSU Labels

Do Not Confuse It With Flex Slot

Huawei / xFusion Related Models

Summary

References

Common CSPS Power Supply Models

HPE Common Slot Option Numbers

Common Models Seen on PSU Labels

Do Not Confuse It With Flex Slot

Huawei / xFusion Related Models

Summary

References

M.2 Key E, Key B, and Key M Pinout Notes

01 Socket 1 - Key E

Pinout Description

Notes

02 Socket 2 - Key B

Pinout Description

Host Interface Configuration

Notes

03 Socket 3 - Key M

Pinout Description

Notes

04 Quick Summary

References

Intel ATX12VO Power Connector Pinout

Why ATX12VO Exists

Connector Difference

Practical Notes

Summary

PCI-E 6-Pin and 6+2-Pin GPU Power Connector Pinout

Why Extra Power Is Needed

6-Pin And 6+2-Pin

Power Capacity

Practical Advice

Summary

`+12VSB`

`PSON#`

`PWOK`

`PMBus_SDA` / `PMBus_SCL`

`A0` / `A1`

`SMBAlert#`

`SMART_ON` / `CR_BUS#`

`+12V Remote Sense` / `+12V Return Sense`

`+12V Share Bus#`

`PRESENT#`

`VIN_GOOD` / `PS_KILL` / `NC`