Wire library: wrong assert on device address

Projects Networking, Protocols, and Devices
1

Hi,

I'm trying to interface with NXP's PCA9532, but get the following error right before sending the first byte:

assertion "(address & 0x80) == 0" failed: file "../source/twi.c", line 261, function: TWI_StartWrite

It looks like the Wire library expects the MSB of the address to be 0, whereas the PCA9532's datasheet (http://www.nxp.com/documents/data_sheet/PCA9532.pdf) clearly states that it must be 1 (it's the MSB of the fixed part, not even user configurable).

This assertion should be removed.

Thanks,

cc

2

The slave address is a 7-bit address which is shifted left by the TWI library. Thus it should be zero. You have to shift it right by one when calling the library.

3

Ahh, because the LSB in the 8-bit address determines transfer direction. Got it, thanks!