> On Jan 31, 2025, at 1:44 PM, Steve Lewis via cctalk <cctalk@classiccmp.org>
> wrote:
>
> Neat stuff. So what got me started (this year) dealing with RS232 is
> trying to figure out a means for doing file-stream data exchange with the
> Commander X16 (which is using a dual 16550 modern-make UART and ~14MHz
> clock). It doesn't have a native terminal software yet with something like
> YModem implemented. Which I've found YModem faster over "wireless serial
> connection" (serial adapted to WiFi, so varied data rates over time) and
> ZModem being faster over wired (null modem) connections (apparently since
> ZModem has particular ACK-timeout requirements, which favors a reliable
> data exchange rate).
>
> So while some protocol gets developed for that system, I experimented with
> other actual vintage system trying to "talk to" a modern PC (where "modern
> PC" is a 3GHz i7 laptop). For the actual task of transferring files, there
> are many other better options, but I still wanted to "push the envelope" of
> what classic RS232 could do on these systems.
>
> And it was interesting that even modern-PC to modern-PC, it only handled
> 460Kbps. But it causes two "opposite" questions:
> 1) How is it even doing over 115.2Kbps? (is that still "RS232"?)
Sort of no, because RS232 isn't specified for data rates that high. I forgot
what the formal limit is, though actual implementations work well above the
specified speed and distance limits. In my DDCMP work I've done RS232
signaling at several hundred kbps.
But mostly "not applicable".
RS232 isn't a UART standard, or a standard for data at particular speeds.
Instead, it is an electrical signaling standard. The main thing about RS232 is
that it specifies a set of interface signals, and electrical parameters for the
signals. For example: drivers generate bipolar signals within some voltage
range, receivers handle bipolar signals within another (larger) voltage range,
with overvoltage tolerance, etc.
Sometimes people speak of RS232 in connection with TTL or other unipolar
signaling voltages. That can't be correct because RS232 specifically excludes
0 volts as a valid signal level.
paul
