OLIMEX© 2015
A20-SOM user's manual
SD/MMC connector
Pin # Connector signal name
Wire name (processor pin)
1 DAT2/RES
SD0-D2 (K19)
2 CD/DAT3/CS
SD0-D3 (K20)
3 CMD/DI
SD0-CMD (L19)
4 VDD
SD_VCC
5 CLK/SCLK
SD0-CLK (L20)
6 VSS
GND
7 DAT0/DO
SD0-D0 (M19)
8 DAT1/RES
SD0-D1 (M20)
9 CARD DETECT(SYMBOL)
SD0-DET# (B6)
13 GND
GND
6.4 Power pins for external power supply
The recommended way of powering the board are the power pins located on the UART0 connector.
They are suitable for 5V DC external power supply unit. The required current may vary depending
on the peripherals connected to the board. The power supply should be capable of providing at least
0.5A of current.
The UART0 connector features also the pins suitable for serial communication with the board. For
the powering, we are only interested in pins 5VEXT and the pin next to it – GND.
The signal names are printed under the pins, make sure to inspect the names before connecting the
supply.
More info about the power supply can be found in chapter 5 of this manual.
6.5 GPIO connectors
There are 6 GPIO connectors located on the top side of A20-SOM. They ease the access to
processors pins. These connectors (except for GPIO-6) also provide a way to mount the board to a
board with peripherals.
Important: boards revisions prior to revision C have only 5 x GPIO connectors. The 14-pin GPIO-6
connector is not available.
Below you would find tables with the signal at each pin. To understand better what each processor
pin does it might be a good idea to refer to the datasheet of the A20 processor. The schematic of the
board of peripherals A20-SOM-EVB might also help you identify the main function of the pins.
To keep the form factor as small as possible the GPIO connectors have 0.05'' step.
IMPORTANT: the connectors are very fragile – if you attempt to disconnect the board by pulling
only one side out it might break! Furthermore – you might bend the board's pins! Use pliers or other
suitable object to disconnect the connectors carefully!
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