-- WhichPin for MCP23017 by John Longworth December 2017
-- Using pins 3 & 4 to be compatible with ESP001
-- 7 segment digit 1 = b + c = 64 + 32       =  96 (0x60)
-- 7 segment digit 2 = abdeg = 128+64+16+8+2 = 218 (0xDA)...
-- DP = 1 added to display to show decimal point

nums = {0x60,0xDA,0xF2,0x66,0xB6,0xBE,0xE0,0xFE,0x9F,0xFC} -- 1, 2 ...0
id = 0   -- Always 0
sda = 3  -- 1 ~ 12  IO index 
scl = 4  -- 1 ~ 12  IO index  
i2c.setup(id, sda, scl, i2c.SLOW)  -- Initialize I2C
device = 0x20
GPIOA  = 0x12  -- I/O register for Port A
GPIOB  = 0x13  -- I/O register for Port B
IODIRA = 0x00  -- Pin direction register Port A
IODIRB = 0x01  -- Pin direction register Port B
GPPUB  = 0x0D  -- Pull Up Register for Port B

function read_reg(dev_addr, reg_addr)  -- Read from Register
    i2c.start(id)
    i2c.address(id, dev_addr, i2c.TRANSMITTER)
    i2c.write(id, reg_addr)
    i2c.stop(id)
    i2c.start(id)
    i2c.address(id, dev_addr, i2c.RECEIVER)
    c = i2c.read(id, 1)
    i2c.stop(id)
    return c
end

function write_reg(dev_addr, reg_addr, reg_val)  -- Write to Register
  i2c.start(id)
  i2c.address(id, dev_addr, i2c.TRANSMITTER)
  i2c.write(id, reg_addr)
  i2c.write(id, reg_val)
  i2c.stop(id)
end

write_reg(device, IODIRA, 0x00) -- Set port A to output
write_reg(device, GPIOA, 255)   -- Write to Port A
-- Set Port B pins as input as 1 e.g. all 8 = 0xFF
write_reg(device, IODIRB, 0xFF) -- Port B all set as inputs
write_reg(device, GPPUB, 0xFF)  -- Set Pull Up Register on Port B

tmr.alarm(1,2000,1,function()  
    i = 255 - string.byte(read_reg(device, GPIOB))  -- Read Port B
    seg = 0
    for loop = 0, 7 do
        if (bit.isset(i,loop)) then        
            seg = loop + 1
        end
    end
    if (seg > 8) then seg = 9
    elseif (seg == 0) then seg = 10 end        
    print(seg)
    write_reg(device, GPIOA, nums[seg])
end)