PCIe M.2 — Key B+E Pinout
An M.2 Key B+E edge combines B and E notches at positions 12–19 and 24–31. It is not a standard PCI-SIG dual-key designation.
Electrical warning: a board with both notches may fit mechanically in Key B and Key E sockets, but their pin assignments are not interchangeable. Several remaining contacts connect a signal in one socket to ground, power, or a different function in the other. Use this geometry only with a complete, product-specific electrical definition.
Connector overview
| Property | Value |
|---|---|
| Connector family | Custom PCI Express M.2 / NGFF module edge |
| Notches | Key B positions 12 to 19 and Key E positions 24 to 31 |
| Contacts | 75 positions; 59 electrical contacts after both notches |
| Mechanical fit | May physically fit a Key B or Key E socket; this does not establish electrical compatibility |
| Standard status | No PCI-SIG Key B+E module profile identified; use only as a documented custom implementation |
| Intended use | Breakout, test fixture, or purpose-designed adapter |
| Supply | Depends on the selected host mapping; do not infer it from the notches |
Key B is associated with Socket 2 applications such as WWAN, SATA, USB, and limited-lane PCIe. Key E belongs to Socket 1 and is mainly used for wireless connectivity. Removing both keying zones does not create a shared electrical pinout.
Contact diagrams
Top side — odd positions
Bottom side — even positions
Contact-position reference
The diagrams document contact numbering and notch geometry only. There is no universal B+E signal assignment to place in a conventional pinout table.
| Side | Positions present | Positions removed |
|---|---|---|
| Top / component side | Odd positions 1–11, 21–23, and 33–75 | Odd positions 13, 15, 17, 19, 25, 27, 29, and 31 |
| Bottom side | Even positions 2–10, 20–22, and 32–74 | Even positions 12, 14, 16, 18, 24, 26, 28, and 30 |
The two notches remove sixteen positions in total. Verify the actual copper pads in the manufacturing data because an absent pad is part of the product’s safety and compatibility definition.
Why the B and E pinouts cannot be merged
The examples below compare standard Key B and Key E socket assignments. They show why a generic B+E electrical mapping would be unsafe.
| Contact(s) | Key B use | Key E use | Design consequence |
|---|---|---|---|
| 1 | CONFIG_3 | GND | Different functions |
| 3 / 5 | GND | USB 2.0 D+ / D− | Direct signal-to-ground conflict |
| 7 | USB 2.0 D+ | GND | Direct signal-to-ground conflict |
| 9 / 11 | USB 2.0 D− and GND | SDIO clock and command | Data/ground-to-SDIO conflicts |
| 21 / 23 | Configuration and GPIO | SDIO wake and reset | Different control functions |
| 35 / 37 | PCIe lane 1 or USB 3 transmit | PCIe link 0 transmit | Pair serves a different link or interface |
| 47 / 49 | PCIe/SATA transmit pair | PCIe reference clock | Data-to-clock conflict |
| 53 / 55 | PCIe reference clock | PCIe clock request and wake | Clock-to-sideband conflict |
| 64 | Wireless coexistence receive | Optional 1.8 V I/O supply | Signal-to-power conflict |
| 71 / 73 / 75 | GND, GND, and CONFIG_2 | PCIe link 1 reference clock and GND | Clock-to-ground conflicts |
This comparison is a compatibility warning, not a replacement for either standardized pinout. Use the dedicated Key B reference and Key E reference when designing for one socket type.
Safe design approach
- Select the one socket mapping the product actually targets: Key B or Key E.
- Treat the second notch as a mechanical feature only unless a controlled host ecosystem defines otherwise.
- Remove or isolate every pad that could touch an incompatible socket contact; firmware cannot prevent a hard electrical conflict.
- Verify power, ground, reset, clocks, high-speed pairs, I/O voltages, and reserved contacts against both schematics.
- Add labeling or another mechanical interlock so the board cannot be inserted into an unsupported socket.
A passive analysis fixture for both socket types should keep their mappings separate through selectors, isolation, or mutually exclusive assembly options. A straight-through board is not a safe universal adapter.
Connector orientation
- The diagrams show the module contact edge, not the socket solder pads.
- The top/component side carries odd-numbered positions; the bottom side carries even-numbered positions.
- The Key B notch replaces positions 12–19; the Key E notch replaces positions 24–31.
- A socket footprint may appear mirrored compared with the module. Follow the connector manufacturer’s recommended PCB footprint.
Common mistakes
- Treating B+E as a standardized dual-key option comparable with A+E or B+M.
- Assuming that mechanical fit guarantees compatible power, ground, or data signals.
- Leaving contacts 3, 5, 7, 64, 71, or 73 exposed without resolving their conflicts.
- Combining Key B and Key E signal names into one table without a product-specific schematic.
- Assuming that two notches protect the board from insertion into an unsupported socket.
- Mirroring the contact numbering between the module edge and socket footprint.
- Hot-plugging an M.2 board without explicit support from the host equipment.
Related connectors
| Connector | Typical use | Compatibility note |
|---|---|---|
| M.2 Key B | WWAN, SATA, USB, and limited-lane PCIe | One possible target mapping, but not electrically interchangeable with Key E |
| M.2 Key E | Wireless connectivity | One possible target mapping, but not electrically interchangeable with Key B |
| M.2 Key A+E | Wireless modules | Documented dual-notch arrangement for compatible Socket 1 modules |
| M.2 Key B+M | SATA and PCIe storage modules | Documented dual-notch arrangement for compatible storage modules |
All PCIe M.2 pinout pages
Compatibility guide · Key A · Key A+E · Key B · Key B+A · Key B+E · Key B+M · Key E · Key M
Official references
- PCI Express M.2 specification overview — PCI-SIG
- M.2 Socket 1 enhancements for Keys E and A+E — PCI-SIG
- Enable PCIe and USB 3.1 Gen1 on M.2 Card Key B — PCI-SIG
- SATA M.2 card-format technical proposal — SATA-IO
FAQ
Is B+E an official M.2 key combination?
No PCI-SIG B+E module profile was identified in the official material reviewed for this page. The label describes a custom edge carrying both B and E cut-outs.
Will a B+E board work in both Key B and Key E sockets?
Not by default. It may fit mechanically, but the socket pinouts conflict electrically. Compatibility requires a board designed and documented for each specific host.
Can I make a passive universal B-to-E adapter?
Not as a straight-through board. Some contacts connect signals to ground or power, while PCIe data and clock pairs occupy different positions.
Why are there 59 electrical contacts?
The B and E notches each remove eight different positions. Together they remove sixteen of the original 75 positions, leaving 59 contacts.
Is the board hot-pluggable?
Do not assume it is. Power down the platform before insertion or removal unless the complete equipment documentation explicitly supports hot plugging.