I’ve used these before in other projects and they worked great. One use was to replace a serial printer on one of our very old test stations at work. I was going to make my own boards to do it and then stumbled on this. Cheaper than the parts I would have had to buy. That’s why when I seen PDDuino, I thought about these.
My plan is to install inside the M100, however I won’t totally get away without additional hardware. I would probably add a buffer so that the serial port can still be used. I would need a level shifter (from 5V and 3.3V) anyway, which is basically a buffer. That should also protect the M100 from any nonsense the Arduino might cause. I had not considered the DTR signal, but you do actually have more I/O. You could use the MOSI or MISO pins at startup. It would do nothing to the SD card because it wouldn’t be chip-selected yet. Or, it is a bit of a hack, but you could tap into one of the two LEDs since it would be inside the M100 and you wouldn’t see the LEDs anyway. And of course, you could break one of the two ground pins and jumper to any other IO pin on the ATMega chip and bring it to that pin. I haven’t studied the code in detail yet, but do you need the DTS/DTR signal for the initial bootstrap process only? Scott M. From: Brian K. White Sent: Saturday, December 19, 2020 10:12 PM To: m...@bitchin100.com Subject: Re: [M100] Model 100 Repair - Keyboard not responding,LCD missing a column I started to try that too a while back, but I think I might have gotten some bad units. I only barely got them to work even just with basic hello-world code or using the pre-installed serial-logging firmware. Maybe I killed the i/o with 5v? One problem with these is you still need to add a rs232 level-shifter, unless you're talking about wiring up directly to the uart, but then it's a very different kind of project, not a plug & play damage-free-towing kind of thing any more. Then again, arduino dev boards need that too, which is what MounT is. Then there is the bootstrap, you'd need to come up with some other way to trigger the bootstrap, or just not have that. There's no other io lines available to use as dsr/dtr. Probably the simplest is just have the tpdd server code recognize a special command that could be sent more or less any time, with no special power up sequence of events and setting up of conditions. The downside is it makes the BASIC code you have to manually enter a bit longer. dlplus originally had something like that, except do something a bit better than exactly what dlplus did, like instead of "XX means do bootstrap" more like "XX means alternate commands prefix" and the command to invoke bootstrap would be XX-something- just like how all TPDD commands are ZZ-something- (I think the original subdirectory extensions made by TS-DOS should have been done that way too instead of using ZZ-previously-unused-number. ZZ-everything- should have been considered off limits and owned by someone else.) I think mComm has something like the original dlplus mechanism too. I do think the microcontroller is up to the task. It's normal off-the-shelf job is already to do exactly the same work, rs232<->sdcard. TPDD is nothing else unless you count the packet checksums. -- bkw > https://www.amazon.com/gp/product/B07T6HBMTZ/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1 > > <https://www.amazon.com/gp/product/B07T6HBMTZ/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1> > > Looks fairly straight-forward so far. > > Looks small enough that one could mount right inside the M100 in the > option ROM area. There is also a bit of room just above the barcode > reader port. It may fit there, exposing the microSD card. -- bkw
