This could be why the cables that club100 used to offer had loop backs on both RTS/CTS and DTR/DSR. But having a full null cable and the software driving it properly works every time. Strange that the 200 is an odd duck.
On Sun, Oct 6, 2019, at 8:40 AM, Russell Davis wrote: > Thanks for doing that. > while trying to workout what was going on I stumbled across > https://www.web8201.net/files/LIBRARY_web8201/M100SIG/Lib-10-Tandy200/NULMDM.200 > which said tie the RTS/CTS together for the T200 which seems to be what you > worked out. > -Russell > > On 10/6/2019 10:47 AM, Kurt McCullum wrote: >> Guys, I did some testing on my T200 to figure out the whole serial port >> wiring issue. >> >> Test 1: >> 1. Write a test application to open the serial port on the PC with DTR/DSR >> and CTS/RTS disabled >> 2. Go to TELCOM on the T200 >> 3. STAT 98N1ENN >> 4. TERM >> 5. Press any key on the T200 and it freezes. >> >> Test 1: >> 1. Write a test application to open the serial port on the PC with CTS/RTS >> disabled but DTR/DSR enabled >> 2. Go to TELCOM on the T200 >> 3. STAT 98N1ENN >> 4. TERM >> 5. Press any key on the T200 and it freezes. >> >> Test 3: >> 1. Write a test application to open the serial port on the PC with CTS/RTS >> enabled but DTR/DSR disabled >> 2. Go to TELCOM on the T200 >> 3. STAT 98N1ENN >> 4. TERM >> 5. Press any key on the T200 and all data is sent to the PC and sent back >> to the T200. Works perfectly. >> >> I Then tested to see if TELCOM is actually using RST/CTS. For this I wrote a >> small application to send a large file to the T200 with Xon/Xoff turned off. >> I then put a bit of code in place to see if the RTS/CTS flags were ever >> changed by the T200 to tell the PC to stop sending. What I found was that >> the T200 never sent a flag to the PC signaling to pause sending data due to >> the buffer being full. This caused garbage on the screen. >> >> So, what I can conclude from all of this is that the T200 serial port >> hardware MUST have the RTS/CTS active or it will freeze the hardware. But >> the TELCOM application does not use those signals to halt data transfer when >> the buffer is full. Instead it relies on Xon/Xoff. Hope that clears things >> up a bit on the mystery of the T200 serial port. >> >> Kurt
