Andrew has been kind enough to spend time exchanging emails, suggestions and reviewing diagnostic results, hoping that we can get my interface working. We don't know if there is a peculiarity with the 3178, some code that could be improved in Andrew's code, or some hardware problem in my interface shield.
He has added instrumentation, suggested changes I can make to the code and puzzled along with me at the behavior we are seeing.
SYMPTOMS AT THIS TIME
When attempting a POLL, which is a one word command issued to the terminal that either indicates it is idle or signals that some action key or other condition has occurred that should be handled by issuing further commands such as READ, we are receiving an invalid message request error.
Having put a pause into the program, after it initializes the link down to the Arduino but before it transmits a POLL, I can see that something is triggered and we fail before even sending the POLL. A message is sent over the coax during the link initialization and receives a response from the terminal.
In some cases, it crashes before the pause, but other times I get a chance to send the POLL. That data begins to be received by the Arduino (scoping the Rx pin) but almost immediately it sends some kind of rejection message to the laptop on Tx and we fail. There is no POLL message sent over the coax, it is blocked in the Arduino.
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