Command Byte; Pca9554 Register 0 - Advantech ITA-5831 Series User Manual

Table 6.2: Pin Define
n.c. -
6.2.1

Command byte

Table 6.3: Command Byte
Command
0
1
2
3
The command byte is the first byte to follow the address bute during a write
transmission. It is used as a pointer to determine which of the following registers will
be written or read. PCA9554 has in all 4 registers to control GPIO.
6.2.2

PCA9554 Register 0

The register is a read-only port. It reflects in incoming logic levels of the pins, regard-
less of whether the pin is defined as an input or an output by Register 3. Writer to the
register Have no effect.
The default 'X' is determined by the externally applied logic level, normal '1' when no
external signal applied because of the internal pull-up resistors.
Table 6.4: Register 0 – Input Port register bit description
Bit Symbol
7 I7
6 I6
5 I5
4 I4
3 I3
2 I2
1 I1
0 I0
If one GPIO Pin is set to Input, you can read input value from the bit that register 0
corresponds to.
-
Protocol
Read byte
Read/Write byte
Read/Write byte
Read/Write byte
Access Value Description
Read only X Determined by externally applying logic level
Read only X
Read only X
Read only X
Read only X
Read only X
Read only X
Read only X
61
3,8,13,18 Not connected
Function
Input Port register
Output Port register
Polarity inversion register
Configuration register
ITA-5831 User Manual