Trouble with the MCP23xxx module

Hi there!

I'm trying to interface and Espruino Pico with an MCP23017 and I'm running into a little trouble with the I2C communication (I2C2, pins B10 & B3, MCP device address 0x20)

The error I'm getting is as follows:

Uncaught InternalError: Timeout on I2C Write Transmit Mode 2
 at line 1 col 43
{this.i2c.writeTo(this.i2ca,c,[a&255,a>>­8])}

I've tried manually reading data from the MCP chip and that works as far as I can tell, my original assumption was incorrect wiring but I've been over half a dozen times and everything looks sound, 10k pullup resistors included on the i2c lines etc, and I can read data from the chip.

The problem only seems to occur when something tries to write to the chip, I've tested two different chips both giving the same error, does anyone think they could lend me a hand with this? It'll likely be something forehead-slappingly simple I've overlooked but on the off chance it isn't, I figured I'd post here

Cheers!

-Josh