VersaLogic VL-EBX-37 Reference Manual page 43

;Configure MCP23S17 register IODIRA for outputs
MOV
MOV
OUT
MOV
MOV
OUT
MOV
MOV
OUT
CALL
;Write 55h to MCP23S17 register GPIOA
MOV
MOV
OUT
MOV
MOV
OUT
MOV
MOV
OUT
CALL
BUSY: MOV
IN
AND
JNZ
EBX-37 Reference Manual
DX, CABh
AL, 00h ;SPIDATA1: 00h for outputs
DX, AL
DX, CACh
AL, 00h ;SPIDATA2: MCP23S17 register address 00h
DX, AL
DX, CADh
AL, 40h ;SPIDATA3: MCP23S17 write command
DX, AL
BUSY ;Poll busy flag to wait for SPI transaction
DX, CABh
AL, 55h ;SPIDATA1: data to write
DX, AL
DX, CACh
AL, 14h ;SPIDATA2: MCP23S17 register address 14h
DX, AL
DX, CADh
AL, 40h ;SPIDATA3: MCP23S17 write command
DX, AL
BUSY ;Poll busy flag to wait for SPI transaction
DX, CA9h
AL, DX ;Get SPISTATUS
AL, 01h ;Isolate the BUSY flag
BUSY ;Loop if SPI transaction not complete
Interfaces and Connectors
37