Yes, in the early days of Radio Shack computers, this was a common practice to use the flat ribbon cable, originally designed for "internal interconnects" in mini- and mainframe computers (housed in large grounded metal cabinets), to connect to external peripherals in the "hobby market". This kind of device connection is what killed the TRS-80 Model I when FCC testing for "emissions" was required on the greatly expanding personal computer market.
Often times every other wire was connected to "ground" to minimize "crosstalk" between signals, but not always, depending on the usage. By the mid '80s, a lot of the printer cables were shielded in round cords and then later ferrite "donuts" were added to reduce unintended emissions by the cables. The 1988 Radio Shack catalog shows that "shielded" printer cables were for the IBM compatible computers (with DB-25 connectors), but the flat ribbon cables were still available for the earlier computers. In looking at a Radio Shack catalog of the period, I see that they also sold 12' flat Centronics Printer cables, but at that distance, the interelectrode capacitance and inductance would require driver ICs with pretty heavy current output. So would be pretty marginal for a M100 with its "all CMOS" hardware. Regards, PeterN On Mon, Jul 13, 2026 at 3:50 PM B9 <[email protected]> wrote: > Radio-Shack's six foot printer cable was unshielded and untwisted? I > wouldn't have expected that to be reliable. > > Am I overly cautious? Or was it perhaps only meant for very low speeds? > Did Radio-Shack at least ground every other wire in the ribbon to reduce > crosstalk? > > --b9 > > P.S. Probably not relevant, but I wonder if the level of background > electromagnetic noise has changed in the last fifty years. > > > On July 13, 2026 2:33:37 PM PDT, Peter Noeth <[email protected]> wrote: > >> Jeff, >> >> If I remember my "70s mini-computer days" correctly, the normal max >> length for Centronics Printer cables was 12'. This was with the round >> cable, consisting of 18 "twisted wire pairs" (one wire signal the other >> wire ground), that was then shielded with an aluminum foil wrap and a bare >> ground "drain" wire connecting it the full length to the metal shells of >> the connectors. >> >> Doing the same with simple flat "ribbon cable" I would expect that >> Radio Shack's 6' length would be the maximum, as they tested functionality >> with that length (but not FCC compliance). Radio Shack used that cable for >> all of their computers, with the "business machines" usually connected to a >> printer on a floor stand, so the 6' length would be appropriate, and for >> connecting a "home computer" with an Epson MX-80 size printer on the same >> tabletop, the cable would just drape down behind the table. >> >> But for portability with the M100 (or T-102 / T-200) I would think a 3' >> cable would be better, especially if you use its original TRP-100 printer >> (or some other portable printer of similar size), as it would be more >> convenient to roll up the cable to pack in a computer bag. >> >> The one I made to use with my Seiko DPU-414 printer is 34" long. For me >> this is long enough to use the computer in my lap while watching T.V. and >> have the printer sitting on the end table. >> >> Regards, >> PeterN >> >> On Mon, Jul 13, 2026 at 1:10 PM <[email protected]> >> wrote: >> >>> >>> Message: 1 >>> Date: Sun, 12 Jul 2026 18:56:53 -0500 >>> From: [email protected] >>> To: [email protected] >>> Subject: [M100] Ideal length for M100 printer cable? >>> Message-ID: <[email protected]> >>> Content-Type: text/plain; charset="us-ascii" >>> >>> Hi all, >>> >>> >>> >>> I had someone ask about acquiring an M100 printer cable a few weeks ago >>> and >>> was surprised how much they were going for on eBay. I have an original >>> cable >>> which is 6' long, which is a bit too long, I think. I picked up some >>> Centroincs connectors and just made a 3' one which is fine for sitting >>> the >>> M100 next to a CGP-115 or larger printer but perhaps not for having the >>> printer sitting away from the M100. >>> >>> >>> >>> What do you think the ideal length is? 3', 4', 5', 6' or perhaps just >>> offer >>> then in either 3' or 6'? >>> >>> >>> >>> Jeff Birt >>> >>> (Hey Birt!) >>> <big snip> >> >>
