I'm trying to reverse engineer the SPI communications between two chips. But, it's not clear who's master and who's slave.
I've found the chip select. Without lifting any pins or cutting traces is there a way to detect which end is asserting it?
The chips are:
CC1110 (SoC radio) and CY7C63803 (USB MCU). The chip select comes off of the SSEL (slave select) line on the CY7C63803 and into a GPIO pin on the CC1110.
The CY7C63803 is an SOIC, so I could lift a leg, but I don't want to break it.
Best Answer
It's difficult to use a GPIO pin on a slave device as a chip select. If the chip select signal is not detected soon enough at the slave device after it is asserted you can miss the data that the master is clocking out. Since the CY7C63803 has its SSEL pin connected to the chip select line my guess is that it is the slave. The CC1110 is probably the master. You will probably need to lift a pin on one of the devices to know for sure.