We are using a TM4C123BE6PZ to interface to a MicroChip MRF24J40 wireless SPI module. The operation is quite satisfactory at -40C-82C temperature range. But we see the SPI voltages drop from 3.3V to ~1V at about 82C. Our range is -40 -> 85C. It appears the TM4 is reading zeros.
So we are trying to ferret out which chip is dragging the voltage dow off of the SPI bus. We are cutting the Master In Slave Out line now to see what happens.
I am using the following code to initialize the SPI port on the TM4:
//GPIOPinConfigure(GPIO_PA3_SSI0FSS); // use other pin for CS
ROM_GPIOPinTypeSSI (GPIO_PORTA_BASE, GPIO_PIN_5 | GPIO_PIN_4 | GPIO_PIN_3 | GPIO_PIN_2);
PA3 is not connected to anything.
For all the examples I found in StellarisWare examples, the GPIOPinConfigure calls are there (I use another pin for CS) but the GPIOPinTypeSSI call is not in the examples.
Does setting a pullup on the RX pin going to help? Or does that only apply if the PA4 pin is configured as an input?
Both parts are rated to 85C.
There are no components between the TM4 and MRF chip. No pullups or pulldowns.
We are using G4 silicon.