' i2c_pcf8574.bas
Dim integer k1=&b10101010,k2=&b01010101
SetPin 6,7,i2c
I2C open 100,100
Do
 I2C write &h20,0,1,k1: I2C write &h12,0,1,k2: Pause 500
 I2C write &h20,0,1,k2: I2C write &h21,0,1,k1: Pause 500
 If Inkey$="x" Then Exit
Loop
I2C write &h20,0,1,255: I2C write &h21,0,1,255 ' turn off

mode 1
option autorun on
OPTION EXPLICIT
OPTION DEFAULT NONE

dim integer porta_bits,portb_bits
'SETPIN gp20, gp21, I2C
'I2C OPEN 100,100

const mcp23017 = &h20 ' A2, A1, A0, R/W all connected to 0V
Const i2caddr=mcp23017
const IODIRA = &h00 ' Port A IO Direction register DEFAULT = I/P
const IODIRB = &h01 ' Port B IO Direction register DEFAULT = I/P
const IOCON = &h0A ' IO Expander config register - address &h0B accesses  same register
const GPIOA = &h12 ' Port A General purpose register
const GPIOB = &h13 ' Port B General Purpose register
const OLATA = &h14 ' Port A latch register
const OLATB = &h15 ' Port B latch register
const GPUPA = &h0C ' Port C pull-up register
const GPUPB = &h0D ' Port B pull-up register
'
I2C WRITE MCP23017,0,2,IODIRA,255 ' set direction to input
I2C WRITE MCP23017,0,2,IODIRB,255 ' set direction to input
I2C WRITE MCP23017,0,2,GPUPB,&hff ' set weak pullups on all
'
Font 5
CLS
'
Do

'then when you read:
'I2C WRITE MCP23017,0,1,GPIOB ' set the register to read
'I2C READ MCP23017,0,1,portb_bits ' read the B port
get_portb_bits
text 0,20,bin$(portb_bits,8)
text 0,60,str$(portb_bits)
Pause 100
Loop

sub get_portb_bits
I2C WRITE MCP23017,0,1,GPIOB ' set the register to read
I2C READ MCP23017,0,1,portb_bits ' read the B port
end sub

Dim integer inp(2)
SetPin 6,7,i2c
SetPin 34,dout: Pin(34)=1 ' power the PCF8575
I2C open 100, 1000
Do
  I2C read &h20,0,2,inp()
  Print Hex$(inp(0));"/"Hex$(inp(1));" ";
  Pause 3000
Loop