Roger Meier's Forums

I am seeing the following problem which I do not think is related to the 6809 SBC. The SBC is a dead simple machine, a 1MHz 6809, with a serial port controlled by an ACIA (6850) which is crystal locked running at 9600,8,N,1. No interrupts, no DMA, 52k of memory available running the very old and well known monitor PTMon (running from ROM) which is patched for the I/O address of the ACIA. Communication between my PC (Win11/Pro 24H2 build 26100.7840) and the SBC is solid using a USB to serial converter. There is no flow control of any kind, and I have added some delay at the end of the line to allow the processing at the end of a line to catch up. This is reliable except when it comes to file transfers from the PC to the SBC which crashes if too many characters are sent from a file. I can send the CoolTerm config file if that is useful. And sample S19 files as well if useful.

The symptom is this:
Send a raw file via menu -> connection, file is received correctly. Try another file and the transfer crashes, and Coolterm must be closed and opened to restore the send capability. Several smaller files can be sent, but eventually the limit is reached and the transfer crashes. Disconnect/Reconnection and Clear the data do not restore operation. CoolTerm must be closed and restarted.

Any assistance gratefully received.

Regards,

Hi,

I recommend also adding a delay after each character (i.e. "Use transmit character delay") in addition to the transmit line delay. The input buffer running on your 6809 may not be deep enough (or fast enough) to keep up with characters arriving in rapid succession. It might be fast enough when typing, but not necessarily when sending a raw file with will send the text as fast as possible unless delays are added. The ACIA 6850 can only buffer 1 character at a time, and it needs to be fetched by software before the next one arrives. If something slows the software down for any reason, then you might start losing characters.

As an example, I'm using a character delay of 30ms and a line delay of 100ms when I'm sending text to MBASIC running on my Altair simulator. Anything less than that results in characters getting lost.

Another thing to check are the line terminations in the file you are sending. Does your 6808 expect CR+LF? or just CR? or just LF? The line terminations in the file you are sending need to conform with what your target expects. I have has issues with files where the line terminations was incorrect.

I hope this helps.

Roger