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ff-mcp23s17: Successful Output Test

I was able to set the GPIOs to output mode and to set the GPIOA pins to pattern 10101010. Here is me testing it with a voltmeter:

Arduino Nano driving an MCP23S17 GPIO Expander module

It turns out that I was sending SPI signals correctly, but that I had make a mistake in the register data I was sending. The IODIRA register, which sets the pins to input or output, requires a 1 for input and a 0 for output. I had assumed it was 1 for output.

MCP23S17 data sheet snippet: IODIR

I have found that if a MC periphal is not doing what is expected, the problem generally comes down to one of five issues:

You have issues with your power supply or voltages.
You have wired the pins incorrectly.
You have your communication settings wrong (SPI sampling settings, for example).
You do not properly understand how your control, addressing, or data frames are supposed to be sent or received.
You are not setting a register bit correctly.

Comments

Alaskalinuxuser, 2021-07-14

That's great that you got it figured out! By the way, the link to the data sheet just gives me a permanent failure when I click it.

Alaskalinuxuser, 2021-07-15

Just tested again this morning. It works now.