The reference design for the SX1282 shows series 1k ohm resistors on the SPI bus lines. What are they for? What is their purpose?
Series resistors in bus lines fulfill two purposes:
- they dampen signal ringing/overshoot.
- they limit cascading faults where one IC has a random hardware fault turning the SPI lines e.g. to short circuits to GND. The resistors in that case limit the current e.g. flowing out of the outputs of the microcontroller.
Be careful: the series resistors form a low-pass filter (RC) together with the input capacitance of the receiver pin (typically some pF). This limits the usable SPI clock rate.