Universal EXTension (UEXT) is a connector layout which includes power and three serial buses: UART/Async, I2C, and SPI. The connector layout was specified by Olimex Ltd and declared an open-project that is royalty-free.
As pin variants only affect the outer pins, which are external to the UEXT pins, you can safely use any of the pin variants whilst retaining full compatibility with UEXT.
UX2-GPIO – 4 x GPIO, 1 x UART, 1 x I2C, 1 x SPI:
UX2-I2C – 3 x I2C, 1 x UART, 1 x SPI:
UX2-ALT – 2 x GPIO, 1 x UART, 2 x I2C, 1 x SPI:
UX2-1IS – 1 x 1-WIRE, 1 x INTERRUPT, 1 x UART, 1 x I2C, 1 x SPI, 1 x SOUND-WIRE:
UEXT cabe should be attached to the centre 10x2 pins (leaving 1x2 pins either side; see diagram further down this page).
| UX2 | UEXT |
|---|---|
 |
Vin, Vcc |
 |
GND |
 |
TXD (not RXD) |
 |
RXD (not TXD) |
 |
SDA |
 |
SCL |
 |
MISO |
 |
MOSI |
 |
SCK |
 |
SSEL |
A 7-way 2-row IDC socket (shown below) accommodates both 5x2 (UEXT) and 7x2 (UX2) IDC plugs.
7x2 IDC socket viewed from above, with UX2-1IS pin variant active
The host/master board must ensure the UEXT pins adhere to the UEXT specifications; for example, the 3V3 pin should be able to supply 100mA of current.