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[SC16IS740, SPI] Device not responding (Stable high on SO)

Question asked by Kerem Karatas on Aug 16, 2017

I'm trying to use SC16IS740 as a bridge from SPI to UART, but I'm yet to receive a response from the device as shown in datasheet page 43. There is a stable 3.072 MHz crystal clock visible on the oscilloscope as well.

I've provided an example below. It shows what happens when 10001000 is sent as the first byte (R/W = 1, A=0001, CH1=0, CH2=0, X=0). 0xFF is sent as dummy data to provide clock cycles for the next byte expecting to read a value (all cleared due to reset)

  1. Part of schematic showing how connections are done
  2. Oscilloscope output for SI
  3. Oscilloscope output for CS

  4. Oscilloscope output for SO


Excuse if I mistakenly published in the wrong "place". I am unfamiliar with NXP communities forum structure.

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