Data Rates:
- Baud (for transceiver): 115,200 to 250k (8us, 4us per cycle)
- tPD from trace length is mostly irrelevant (about 150 ps/in of trace)
- Datasheet:
- Rise time 70 ns
- Fall time 80 ns
- 8 us > (70ns + 80ns)
- Theoretical max is 1Mbps for the transceiver, but this can cause instability due to propagation delay
- Clock (for SPI): 5-10 MHz
- Higher speeds increase EMI, reflections, etc.
- Use external crystal oscillator for precision (our STM32 supports up to 50MHz)
- Rough calculation
Downlink:
- Watchdog output (WDO pin, 1 bit): 0 = STM time-out detected, resetting STM32 / 1 = STM time-out not detected
- GPIO for EN (if EN is low, watchdog enabled. If EN is high, watchdog disabled), maybe jumper to control EN
- Brownout: STM BOR supervisor reads voltage and resets (how to send that information to ground?) - BOR reset flag is sent if BOR goes off in Extended interrupt and event controller (EXTI)
- Flags available also for Power on reset
- Motor Driver Faults: (all through SPI to microcontroller then to transceiver)
- CPUV (charge pump undervoltage)
- OCP (overcurrent fault)
- STL (motor stall)
- TF (overtemp warning / overtemp shutdown)
- OL (open load fault)
- SPI error
- Motor Diagnostic Flags (some of these overlap with Motor Driver Faults)?:
- Overcurrent on AOut1, BOut1 (low side & high side)
- Motor Power Saving Mode?
- Overtemp warning + Overtemp shutdown?
- Motor stalled
- Open load detection?
- Voltage line measurements? 3.3V (handled by microcontroller)
- Note: Recommend Thermo to consider temperature data from STM and Motor Driver
- Implement EXTI and NVIC controls to read interruption flags and prioritize violations (Brownout, voltage drops, Watchdog reset,can be flagged and downlinked using these controls on STM32). Also note Reset and Clock Control (RCC) Register on STM.
Uplink:
- Reset motor driver faults (nSleep pin / 20-40 microseconds)
- Set STM modes (Safe, Science, Uplink) - Probably for Controls/Comms (keep here as reminder)