What GPIO pins are used by the Piface CAD shield?

Goswin

There are no schematics that I've been able to find, but the documentation mentions that the IR is on GPIO 23.

The lcd and buttons connect to a mcp23s17 16 bit GPIO port expander, so apart from the SPI pins, the rest of the GPIO is free.

I suspect all the mcp2317 pins are used, as the backlight is controllable, and besides its buried below the LCD, which is soldered in place.

If the GPIO pins were extended, you would have trouble with cases, and the shield/plate covering the LCD, so it needs to be the top of a stack.

A nice option would be to be able to order them without the GPIO plug soldered on, which means you could fit an extension version.

There is a PiRack which I was fortunate to receive before release, and I reviewed it here  PI RACK it gives the ability to set the SPI address.

I modified a Piface Digital and added two rows of single headers, http://www.element14.com/community/roadTestReviews/1452 , however the Picrust or similar might be a better option

The other alternative is to solder wires onto the pads, or fit a plug, etc.

Mark

Mark your post got me desoldering my PiFace and here's the disassembly !

Many thanks for your efforts in 'reversing' the Piface CAD, the python code for the board suggests a connection from the MCP23S17 INTA and INTB pins, do you know which GPIO they are connected to or am I reading the code incorrectly?

Err the Interrupt lines didn't seem to be connected at least according to my paper work also I don't

think there is any interrupt lines on the connector  for the Pi to pick up that interrupt source any way !

Ah, OK, I'm barking up the wrong tree then.

My train of thought was that there is an interrupt on change available on the MCP chip and that the interrupt lines were routed out to a GPIO pin on the Pi. I'll have to rethink

Thank you for replying so quickly.

Yeah I admit that I was expecting an interrupt for the button presses. Having said that if there's no interrupt brought out on the connector then it's just not happening!

I'm assuming that you are essentially meant to poll the chip often enough to detect the key press or it's latched or something and some "magic" is done by the supporting

driver / userland  interface

Goswin, the serial and the other SPI channel are free so you can use these if you can get to the pins.

Are you going to mark your question answered so others can find this in searches and be helped ?!?

John

Seems a shame not to use the feature if it's there or at least bring it out to a jumper somewhere.

I've ordered a Piface CAD now so I'll look at the possibility of adding it.

I've built a working ratsnest version of the CAD from what I can deduce by reading the code and checked it with your schematic when I found it.

I was sure I'd seen interrupts mentioned in the python code but looking again now, I can;t find the piece of code I thought I saw. It was a long, tiring weekend so I could be confused.

{EDIT}

Now I look again, in core.py:

'import pifacecommon.mcp23s17

import pifacecommon.interrupts

import pifacecad.lcd

DEFAULT_SPI_BUS = 0

DEFAULT_SPI_CHIP_SELECT = 1

NUM_SWITCHES = 8'

I see that any of the GPIO pins can be programmed to produce an interrupt either based on a transition or level of a GPIO  at least on newer Kernels  so maybe  you can do something with that.

I'll take another look see if the int pins are plumbed in anywhere after all!

Thank you, I have made a little progress with my ratsnest CAD while my 'proper' CAD is sat in the office waiting for me to get there.

I can read the MCP GPIOA status from the Python shell or in IDLE so I know the MCP is configured and working but none of the examples respond so I can't help think I've missed something in the ratsnest.

I'll be collecting my official Piface tomorrow so with luck it'll all become clear.