Appendix B Digital I/O; B.1 About Digital I/O; B.2 Digital I/O Programming - AXIOMTEK CAPA840 User Manual

B.1 About Digital I/O

The digital I/O on CPU board has 8 bits. Each bit can be set to function as input or output by
software programming. In default, all pins are pulled high with +5V level (according to main
power). The BIOS default settings are 3 inputs and 5 outputs where all of these pins are set to
1.

B.2 Digital I/O Programming

2
 I C to GPIO PCA9554PW GPIO.
2
 I C address: 01001000.
Command byte
Command Protocol
0 Read byte
1 Read/write byte
2 Read/write byte
3 Read/write byte
The command byte is the first byte to follow the address byte during a write transmission. It is
used as a pointer to determine which of the following registers will be written or read.
Digital I/O
Function
Input port register
Output port register
Polarity inversion register
Configuration register
CAPA840/843 Capa Board
Appendix B
Digital I/O
CN1
Pin Signal Pin
1 DI0 2
3 DI1 4
5 DI2 6
7 DO0 8
9 GND 10
Signal
DO4
DO3
DO2
DO1
+5V level
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