Appendix E Digital I/O; Digital I/O Software Programming - AXIOMTEK IMB523R User Manual

Digital I/O Software Programming

 I2C to GPIO PCA9554PW GPIO[3:0] is Output, GPIO[7:4] is Input.
 I2C address: 0b0100100x.
 IOBASE: 0xF040
 Registers:
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.
Register 0: Input port register.
This register is a read-only port. It reflects the incoming logic levels of the pins, regardless of
whether the pin is defined as an input or an output by Register 3. Writes to this register have
no effect.
The default 'X' is determined by the externally applied logic level, normally '1' when no external
signal is externally applied because of the internal pull-up resistors.
Bit Symbol
7 I7
6 I6
5 I5
4 I4
3 I3
2 I2
1 I1
0 I0
Digital I/O
IMB523R / 524R / 525R LGA1151 ATX Motherboard
Function
Input port register
Output port register
Polarity inversion register
Configuration register
Access Value
Read only X
Read only X
Read only X
Read only X
Read only X
Read only X
Read only X
Read only X
Appendix E
Digital I/O
Description
Determined by externally applied
logic level.
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