I've got this radio communication with an RC helicopter. I found that the RX on the heli is using an AVR MCU and a CYRF6989 2.4Ghz chip to communicate with the controller of the heli and translates it to drive the servos and motors.
The MCU and the CYRF chip communicate by SPI. I want to intercept and interpret the signal so I soldered some wires on it. I am able to read the signal (either MOSI or MISO) using an Arduino prototype board. But I am having trouble understanding/interpreting the datastream. So I need a different approach than reading only MOSI OR MISO.
My current situation is that the Arduino is the slave, and it will either read the MOSI or MISO signal, but I can't figure out how I would go about reading the whole 'conversation', so both the MOSI and MISO signal. The only thing I can come up with is to connect MOSI and MISO to 1 wire using a diode (so the MCU and CYRF chip on the RX board aren't getting mixed signals) and read the data flowing over that one wire with the arduino board (using the SPI pins of the Atmega 328P). So MOSI and MISO come in over the same wire, which shouldn't be a problem really, as MOSI and MISO will never occur simultaneously. But the problem with that approach is that I do not have an indication of the origin (MOSI or MISO?) of the signal. It would be the easiest to have to SPI buses on the MCU, but thats against principles of SPI and AtMega2560 doesn't have so either.
Basicly my question is, what is a good approach to intercept the SPI conversation, so I am more able to interpret its meaning?
Best Answer
To fully listen in on a SPI conversation, you need to be watchin all four lines: chip select, clock, MOSI, and MISO. You could possibly do this with two separate SPI peripherals. Both are connected to chip select and clock, with one watching MOSI and the other MISO. The rest is then firmware to interpret the results.