Add support for the old, deprecated MCP23016 expander, too.

[Flameeyes]

The main difference with the '17 is that it lacks advanced interrupt
control features, and pull-up configuration.

This includes changes to DigitalInOut to raise ValueError when trying to
set pull-up configuration as well as pull-down, on the MCP23016 only.

Note that for compatibility with the already existing '17 module, and for
an eventual '18 module, the ports are called A and B, rather than 0 and 1.

[Flameeyes]

This is "intended" on top of #28, in which case this is just a single commit :)

[caternuson]

Is this PR essentially the same as #28 with the addition of the new MCP23016 code?

[Flameeyes]

Yep. I split the two because I think the other one is uncontroversial, and this one I'm not sure. In the sense that I don't know if supporting MCP23016 (which is no longer recommended, but slightly cheaper) fits into the library's roadmap.

[caternuson]

I'd suggest pausing on this PR and opening an issue for "Adding support for MCP23016". A discussion could then be had there about adding MCP23016 support.

[Flameeyes]

Opened #30.

[Flameeyes]

Now that #28 is merged, this pull request has the single change (MCP23016 support).

[tannewt]

@caternuson Mind reviewing this?

[FoamyGuy]

The details of the code / implementation are a bit above my head still, so I don't think I have much to offer in that area. But I did grab a few of these ICs with a recent DigiKey order with the intention of testing the functionality of this PR with them.

[caternuson]

One minor cosmetic change.

[caternuson]

@FoamyGuy If you can test, that would be great :)

[FoamyGuy]

I was able to get this working. The library changes seem to be working correctly as far as I can tell.

Thank you for adding support for this version of the IC!

I tested all 16 IO pins on output in sets of 4 at a time. And I tested input using external pull up resistor on 1 of the IO pins

I tested with this code:

import time
import board
import busio
import digitalio

from adafruit_mcp230xx.mcp23016 import MCP23016

# Initialize the I2C bus:
i2c = busio.I2C(board.SCL, board.SDA)

mcp = MCP23016(i2c)

pin_nums = [12,13,14,15]
pins = []

pin8 = mcp.get_pin(8)
pin8.direction = digitalio.Direction.INPUT

for pin in pin_nums:
    pins.append(mcp.get_pin(pin))

for pin in pins:
    # Setup pin0 as an output that's at a high logic level.
    pin.switch_to_output(value=True)

# Now loop blinking the pin 0 output and reading the state of pin 1 input.
while True:
    for i, pin in enumerate(pins):
        pin.value = i % 2 == 0
    time.sleep(0.5)
    for i, pin in enumerate(pins):
        pin.value = i % 2 != 0
    time.sleep(0.5)    

    # Read pin 1 and print its state.
    print("Pin 8 is at a high level: {0}".format(pin8.value))

It would probably good eventually to add this variant to the example script. And possibly document the required wiring setup to get it working

[Flameeyes]

Can this be merged as is for now, or should I try adding more documentation first?

I mean technically the MCP23018 is still missing too, but I don't have one of those at hand…

[caternuson]

Nah, let's just merge this. Thanks for testing @FoamyGuy

[caternuson]

@FoamyGuy wanna make a release?

[FoamyGuy]

Yep, will do.