This project <https://zx81keyboardadventure.blogspot.com/2017/08/model-100-micro-sd-card-reader-mytesed.html> gave me the idea to try my project. He is using 1200 BPS as well. But, strangely, he's using 7 bits and ignoring parity, as well as turning off XON/XOFF.
I'm in control of what the Arduino sends, so I know it's not sending an XOFF. Now that doesn't mean that something else is happening and an XOFF is getting sent to my T102. I'm running on the assumption that the Arduino, being much newer hardware, should have no trouble keeping up with the T102. I think that's a correct assumption, but it's still an assumption. If I spent the resources to get an RS-232 monitor, I might be able to see which end is having the issue, but it's not worth it to me right now. On Thu, Nov 30, 2017 at 5:30 PM, Mike Stein <[email protected]> wrote: > Sounds nice! > > Nothing wrong with using a 'shifter' and I'm just picking a nit, but the > issue with interfacing RS232 to TTL in this case is not so much the voltage > but the polarity. The ModelT outputs +5V to -5V and some TTL-type inputs > don't like a negative voltage even if it's current limited as it is in the > Model T's; it's recommended to clamp the -5V at 0V somehow, which your > shifter takes care of. Receiving a TTL-level signal on the ModelT will > usually work, but a bipolar RS232 is somewhat more reliable. > > Still odd that you can't go above 1200bd; have you tried disabling XON/XOFF > (with the loopbacks connected) in case the Arduino is sending an XOFF but > never an XON? Since nothing changes on the T102 except the speed it would > suggest that the other end can't keep up for some reason and a buffer is > filling up somewhere, unless there's an issue with parity or framing. -- Ron Lauzon - rlauzon at acm dot org Homepage: http://webpages.charter.net/rlauzon/ Weblog: http://ronsapartment.blogspot.com/ TRS-80 Pocket Computer 2 - TRS-80 Pocket Computer 4 - TRS-80 Model 100/102 Some people like to work on old cars. But old computers are cheaper and don't require a big garage.
