On Tue, Jun 22, 2021 at 6:32 AM Grant Taylor via cctalk <cctalk@classiccmp.org> wrote: > > I would love to see REAL RS232 on a RBPi, probably even the original > > MMJ from DEC for keyboard & mouse > > What is a /real/ RS-232? How does it differ from USB-to-RS-232 and / or > bit banging GPIO lines?
The OP said he meant with "real" connectors, but in my case, I've encountered strange buffering issues with USB serial dongles (since they are really block-mode devices, not character-at-a-time) and I've definitely had problems supporting lines with odd parameters (especially speeds slower than 300 baud or with 5-bits-per-char, like one would use for a Model 19 or Model 28 teletype). The hardware UARTs on AVR processors implement those juse fine (though for "50 baud", you often have to put a slower crystal on the processor because the 16-bit divisor overflows at 16-20MHz). The "soft serial" libraries often just hard-code 8-bit implementations. Fine for modern stuff but I have uses for connecting to electromechanical serial devices. In terms of a CRT terminal, though, most modern serial implementations are fine. -ethan
