RE: IR thermometer complications

koudelad — Thu, 08 Mar 2018 11:34:27 GMT

I would just like to post an update in case anyone stumbles upon this post.

I didn't get an additional answer from Melexis nor their distributor, but I found an application note that is not available on the official Melexis site (no idea why). It describes the details of the communication in more depth than the datasheet: https://www.pololu.com/product/1061/resources

It confirms what has been written above, the PEC is computed always from all the bits on the data bus (excluding the start, repeated start and stop bits).

What also helped me a lot: there is an application report from TI, SLAA249 Implementing SMBus Using MSP430 Hardware I2C, which also contains firmware examples for MSP430. I used a PSoC 4 and the adjustments made to the SW implementation of the CRC8 calculation is really cosmetic.

I implemented the functions in the Visual Studio, tested and debugged and then ported to the PSoC in order to save time spend debugging.

David

RE: IR thermometer complications

shabaz — Mon, 22 Jan 2018 12:40:14 GMT

Hi David,

I think it's worth asking Melexis for example code. They take into account the address and the command bytes too, as far as I can tell. So, the PEC should include those bytes too (I could be wrong).

Anyway, I tried for about 10 minutes too, and didn't get very far (I could get the correct PEC for one of the sequences in the datasheet, but for the wrong reasons, and it fails for the other sequences).