MCP23017 (ControlEverything) - Output Pin Status always 0

Question

WOOHOO! MY first official foray into micro controllers!

Its a lot of fun sofar but I am a bit stuck at the following:

I'd like to read the status of PINs configured as Output, in other words, Did I set the pin to High or Low?

I've built my own source in python 2.7 and used the examples I got from ControlEverything.com (bought the entire board from them). I'm using smbus and in short I've set the entire Port-A bank to Output, then riased them to High. I can see my LED turn on at this point.

import smbus

bus = smbus.SMBus(1)

bus.write_byte_data(0x20, 0x00, 0x00) #set Port-A as output
bus.write_byte_data(0x20, 0x12, 0xFF) #set Port-A to High
#LED turns on

status = bus.read_byte_data(0x20,0x12) # read the bus I just set to 0XFF
print "%s return value: %d"  %("0x12",status)

At this point I always get 0 as my return val, although my LED is burning brightly.

Am I reading the wrong register or is there more at play here?

Answer 1

For future reference (for people starting out, like myself) the problem was solved when I properly set the addresses on the A0 - A2 pins. Once that was set up I could see a change on the GPPU pins from 1 1 1 1 1 1 1 1 to 1 0 1 1 1 1 1 1 when there is an input.

Do'h

Answer 2

There is a difference between reading GPIOA and OLATA. This is just an observation, I don't know the precise rules.

I have LEDs connected to each output of port A.

Result of writing 0 to 255 to GPIOA and reading back GPIOA.

GPIOA (0-255)
 0  0  0  2  0  4  4  6  0  8  8  a  8  c  c  e 
10 10 10 12 10 14 14 16 10 18 18 1a 18 18 18 18 
20 20 20 22 20 24 24 26 20 28 28 2a 28 28 28 28 
20 20 20 22 20 20 20 20 20 28 28 28 28 28 28 28 
40 40 40 42 40 44 44 46 40 48 48 4a 48 4c 4c 4c 
40 40 40 42 40 40 40 40 40 48 48 48 48 48 48 48 
40 40 40 42 40 40 40 40 40 48 48 48 48 48 48 48 
40 40 40 40 40 40 40 40 40 48 48 48 48 48 48 48 
80 80 80 82 80 84 84 86 80 88 88 8a 88 88 88 88 
80 80 80 82 80 80 80 80 80 88 88 88 88 88 88 88 
80 80 80 82 80 84 84 84 80 88 88 88 88 88 88 88 
80 80 80 80 80 80 80 80 80 88 88 88 88 88 88 88 
c0 c0 c0 c2 c0 c4 c4 c4 c0 c8 c8 ca c8 c8 c8 c8 
c0 c0 c0 c0 c0 c0 c0 c0 c0 c8 c8 c8 c8 c8 c8 c8 
c0 c0 c0 c2 c0 c0 c0 c0 c0 c8 c8 ca c8 c8 c8 c8 
c0 c0 c0 c0 c0 c0 c0 c0 c0 c8 c8 c8 c8 c8 c8 ca 

Result of writing 0 to 255 to GPIOA and reading back OLATA.

OLATA (0-255)
 0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f 
10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f 
20 21 22 23 24 25 26 27 28 29 2a 2b 2c 2d 2e 2f 
30 31 32 33 34 35 36 37 38 39 3a 3b 3c 3d 3e 3f 
40 41 42 43 44 45 46 47 48 49 4a 4b 4c 4d 4e 4f 
50 51 52 53 54 55 56 57 58 59 5a 5b 5c 5d 5e 5f 
60 61 62 63 64 65 66 67 68 69 6a 6b 6c 6d 6e 6f 
70 71 72 73 74 75 76 77 78 79 7a 7b 7c 7d 7e 7f 
80 81 82 83 84 85 86 87 88 89 8a 8b 8c 8d 8e 8f 
90 91 92 93 94 95 96 97 98 99 9a 9b 9c 9d 9e 9f 
a0 a1 a2 a3 a4 a5 a6 a7 a8 a9 aa ab ac ad ae af 
b0 b1 b2 b3 b4 b5 b6 b7 b8 b9 ba bb bc bd be bf 
c0 c1 c2 c3 c4 c5 c6 c7 c8 c9 ca cb cc cd ce cf 
d0 d1 d2 d3 d4 d5 d6 d7 d8 d9 da db dc dd de df 
e0 e1 e2 e3 e4 e5 e6 e7 e8 e9 ea eb ec ed ee ef 
f0 f1 f2 f3 f4 f5 f6 f7 f8 f9 fa fb fc fd fe ff 

Code used.

#!/usr/bin/env python

# MCP23017-readback.py

import pigpio

IODIRA=0
GPIOA=18
OLATA=20

pi = pigpio.pi()

if not pi.connected:
   exit()

h = pi.i2c_open(1, 0x27) # Get handle to MCP23017 on I2C bus 1 at 0x27.

pi.i2c_write_byte_data(h, IODIRA, 0) # Set port A as output.

str_GPIOA = ""
str_OLATA = ""

for i in range(256):

   pi.i2c_write_byte_data(h, GPIOA, i) # Write i to port A.

   _GPIOA = pi.i2c_read_byte_data(h, GPIOA)
   _OLATA = pi.i2c_read_byte_data(h, OLATA)

   str_GPIOA += "{:2x} ".format(_GPIOA)
   str_OLATA += "{:2x} ".format(_OLATA)

   if (i % 16) == 15:
      str_GPIOA += "\n"
      str_OLATA += "\n"

print("GPIOA (0-255)\n"+str_GPIOA)
print("OLATA (0-255)\n"+str_OLATA)

pi.i2c_close(h)

pi.stop()