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Fat HP RS-232 extension cable

agentb

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I found this massive HP RS-232 extension cable. Why was it so fat? Did newer cables only run some of the pins in the cable, not all 25, so a thinner cable? Were these HP cables thicker gauge wires or lots of shielding? Just trying to understand why this thing is so hefty!
 

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Chuck(G)

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Not unusual at all for the time. Good quality cable--I recall wiring two rooms of terminals with the stuff from a 500' spool of the HP stuff. Consider, also, the length of your cable--RS232C is a protocol that relies on voltage for signaling, so less resistive drop in beefy cables.
 

agentb

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Gotcha - I figured the longer distance of this cable might have something to do with it and also potentially shielding if you are running a bunch of cables near it.
 

mdh

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But it looks like yours runs all 25 pins, which is quite nice. I had a similar cable about 50 feet long, and never had any issues.
 

sunjar

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I have to say I miss the 80s and 90s, when industrial products were full of sincerity and never hesitated to use materials.
 

agentb

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BTW- anyone have a use for this / want this beast of a cable? It weighs about 4lbs and is 10m (33 ft) long. I don't have a use for it right now.
 

DeltaDon

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Several laptops (Chicony MP975 for one) used the serial port for an external floppy drive via a short cable and used some extra wires, I believe. But none that I know ever needed a 33' long cable.
 

Plasma

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From the link:
Only very few computers have been manufactured where both serial RS232 channels are implemented. Examples of this are the Sun SparcStation 10 and 20 models and the Dec Alpha Multia. Also on a number of Telebit modem models the secondary channel is present. It can be used to query the modem status while the modem is on-line and busy communicating.
 

mdh

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One of the serial ports on the BigBoard II supported the tx / rx clocks, but I've never seen it used.. I basically ignored it.
 

Eudimorphodon

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Having the transmit/receive clock pins present was *reasonably* common on CP/M/S100-era computers. (The NorthStar Horizon has them, for instance.) Quite a few early machines also used some of the extra pins to provide for running 20ma current loop interface devices, but this wasn't an official part of the RS232 standard so a cable set up for one machine wouldn't necessarily work on a different one.

FWIW, the original IBM Async Communications Adapter card for the 5150 falls into that latter category, it uses pins 9, 11, 18, and 25 for the 20ma loop capability. So far as I know this wasn't commonly replicated on clone cards, and of course it went out the window with the 9-pin standard.
 

Chuck(G)

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I've got an HP cable of similar stripe that has a section of the vinyl jacket removed and a grounding clip attached to the shield (woven wire).
I have several 25-pin D-sub B shell straight-through from the PC era. Very useful for devices connected to the printer port.
I'll venture that in the bad old days of Bell 208 modems, that all cables were 25-conductor. Lots of signals on those old sync modems...
 

DeltaDon

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It's been so long since I had an external acoustic modem that I can't remember any issues with connecting them to a computer. About all I recall was that it was a 600 baud or maybe a 1200 baud modem. My DB25 RS232 S-100 systems used the hardware handshaking lines 4,5 & 20, but nothing more exotic and they worked just fine with my modem. About the only issue I remmeber was my phone used a handset with square speaker/mic and I had to purchase a round handset to use the modem. But even my first laptop, a NEC Starlet CP/M based laptop, had a built-in 300 baud modem so I avoided the early day modem issues, I guess.
 
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