The receive buffer on m100 is small and tge screen updates in telcom take so much time that, even with xon/off enabled, you can't go over 600 baud reliably. The in-band software flow control has a minimum round trip time that means that by the time the 100 sends the "stop sending" and the other side gets it and stops, there are too many bytes already in flight and it overflows the 100s receive buffer. It can keep up with 600, 1200 it almost manages but not quite.
With the screen updates turned off you can go higher but 9600 may still be too high. It depends on the software being used on the 100 and the size of any continuous transmissions. TPDD uses 9600 and 19200 reliably only because it operates in small packets and no screen updates. TPDD clients have small fast machine language routines to process the bytes in as few cpu cycles as possible, with no screen updates in the inner loop, and the largest possible packet in the protocol is still under 256 bytes. So even with no flow control, the protocol itself stops transmission anyway and waits for an ack before sending the next packet. You may be able to use 9600 for tnc but only if the software is not also drawing on the screen at the same time it's receiving, and especially if it naturally operates in small chunks with breaks. Using TELCOM, with the screen enabled, and possibly arbitrarily long continuous downloads, you're limited to 600 baud. The machine physically has rts/cts hardware, but nothing in the system rom (including telcom) enables rts/cts. The only software known to use rts/cts is HTERM and I think TBACK, which you can find on bitchen100. That can reliably go over 600 because it has it's own machine language code to operate the uart. Anything else will be limited to xon/xoff. bkw On Sun, Jul 9, 2023, 6:20 PM Jesse Bertier <berti...@gmail.com> wrote: > First time getting my hands on a model T. I am attempting to connect to a > TNC at 9600 baud. I have both matched for 8,N,1 and 9600 baud. TNC works > with other PCs. I’m using TELCOM and set the parameters correctly. What > happens at 9600 baud is the text coming into the m100 is garbled mostly and > on occasion some valid words come across. When I set both to 300 baud, > works perfectly. It seems to be problematic if there’s a solid block of > text coming in, like a string of 20-30 words for example. > > Before I dig into the problem with the service manual and get out the > scope, does anyone know if these are supposed to work well at 9600 or up to > 19,200 ? Or, does the buffer or machine get overloaded at higher rates? > Is TELCOM the issue? > > Sent from my iPhone
