31 Jan
2025
31 Jan
'25
10:55 a.m.
On Jan 31, 2025, at 1:44 PM, Steve Lewis via cctalk
<cctalk(a)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