1
\$\begingroup\$

I'm trying to hack my wireless thermostat to control my heating. I disassembled my unit and found the communication chip ( CC110L - SPI 433MHz). I searched for the datasheet and tried to determine which pin is which. I think I found the right pins and connected it to my digital analyzer, but my readings are strange. My clock signal does not look like a clock signal, and the CSn signal looks more like a clock signal but it does not match the datasheet.

Is it really a clock signal? Because my values do not look right. See attachment please.

enter image description here

\$\endgroup\$
2
\$\begingroup\$

The signal "CSn" really seems to be the chip select signal but what you see is not the truth:

If I interpret the dots in your logic analyzer window correctly you have a sample rate of 25 kHz.

The frequency of the CC110L's SCLK signal can be up to 10 MHz.

If I interpret your screen shot correctly the CSn line is low for more than 40µs but less than 80µs. The CC110L uses 16 clock edges per SPI transfer.

This means the clock frequency actually used is somewhere above 400 kHz - maybe 500 kHz. If 500 kHz is true you'll need more than 1 MHz sample rate to see anything (depending on the duty cycle of the SCLK signal even more). And you should use at least 2 MHz sample rate to see a correct SPI signal.

Using a sample rate of 25 kHz (0.025 MHz) you can see nothing.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.