Thanks for getting back to me. I’ve attached a couple of scope shots that may help.
Ch1 (Yellow) SPI Clock
Ch2 (Green) MOSI
Ch3 (Blue) MISO
Ch4 (Red) Interrupt from ASR-1
When you suggested adding a few hundred millisecond delay before I start clocking in MISO, do you mean a delay between the interrupt from ASR-1 and the beginning of the clock? Right now there is a 60usec delay but I can increase that to a few hundred msec.
It is specific code written for a custom PCB. I can send snippets of the code but I thought the scope traces may help more. I ordered an Arduino Teensy and was planning to use it with your afLib for comparison when it arrives.
I get an interrupt from the ASR-1 about every 0.5sec. After each interrupt, my board sends the Zero Sync and the ASR-1 responds with the 0xaa, every time - very repeatable.