31 Jan
2025
31 Jan
'25
1:55 p.m.
On 2025-01-31 14:44, Steve Lewis via cctalk wrote:
But for other fodder, I'm reading over the async card for the IBM 5110.
Page 12 of this IBM 5110 doc has a block diagram of IBMs version of
"asynchronous card" -
SY31-0552-3_IBM_5110_System_Logic_Manual_197902.pdf
<http://www.bitsavers.org/pdf/ibm/5110/diagrams/SY31-0552-3_IBM_5110_System_Logic_Manual_197902.pdf>
And its manual (from 1978) has some interesting paragraphs (plus how that
system was apparently obsessed with showing text-mode graphs of the error
rates; line quality is apparently still very rough by late 1970's):
SY31-0557-0_5110asyncComm_Jan1978.pdf
<http://www.bitsavers.org/pdf/ibm/5110/SY31-0557-0_5110asyncComm_Jan1978.pdf>
-SteveL
Line quality depended on what you wanted to pay for. Voice grade lines
have a few problems the main ones being the limited bandwidth and echo
suppressors. But in the late 70s when I started with TP equipment, and
probably earlier you could also get "conditioned" lines that had a much
wider bandwidth and no echo suppressors. I recall people running 56K
baud and higher synchronous lines, but they did not use RS232 but rather
they used a V.35 interface. Already at that time people where using
fancy means to increase speed, I recall modems that used phase shift
keying and 90 degree shifts so you could encode 2 bits in every phase
shift by shifting by 0, 90, 180, and 270 degrees. In the late 70 early
80s I know for sure IBM communication controllers supported line groups
where the data would be fired down multiple pipes to get higher
throughput. I also recall dial-up conditioned lines that had a
special phone set on them that you could use to talk to people at the
other end, talking on them was line talking in a tunnel.
Paul.