Re: SUMMARY: ab switch problem.

Ross Binnie (
Thu, 2 Oct 1997 08:11:20 -0400

I use a mechanical AB switch in the same application and it works ok.
Actually I have another T switch downline for 2 printers. The port to
switch cable is very short (about 2'). Switch is made in China. Model
DS252, Importer Startech Computer Accessories Ltd. London Ontario, N6A 1R8.
Selling price varries, I paid CDN$20.00 .
Have had IRQ probs up to here, so tend to stick with the simplest method of
getting things done.

> From: Mark Andrew Nassy <>
> To:
> Subject: SUMMARY: ab switch problem.
> Date: Wednesday, October 01, 1997 8:42 PM
> hardware and software:
> manual ab switch connected to the only printer port of an ibm clone
> windows 95. connectix quickcam and a cannon color printer connected to
> ab switch.
> the problem:
> error message when cornell cuseeme tries to access quickcam. quickcam and
> the printer work fine if individually connected directly to the printer
> port.
> the cause:
> since the printer and the camera work fine with the port this suggests
> problem lies with the ab switch. in order for quickcam or the printer to
> work it is necessary for the ab switch to switch all 25 wires and not
> those necessary for the printer to work. The reason for this is because
> newer printers with bidirectional drivers must read and write to the
> printer port to get the port status. should not all the wires get
> windows95 will have problems scanning the parallel port.
> the solution:
> if you have a free isa slot in your computer purchase:
> (1) ecp/epp/bidirectional parallel port that uses IRQ 5 or 7, for
> $20.00+us, or
> (2) ecp/epp/bidirectional parallel port with a 83 byte buffer that uses
> IRQ's 5, 7, and 9 through 15 for $40.00+us, or
> (3) i/o port combo. card for $25.00us and install any of these in a free
> isa slot.
> the printer should then b connected to lpt2 and quickcam to lpt1. (im not
> sure y it is recommended to connect quickcam to lpt1 and not lpt2
> if you dont have a free isa slot in your computer purchase
> (1) an electronic ab switch. the cost of an electronic ab switch is
> approximately $40.00+us.
> discussion:
> when installing the new card in a free isa slot there is the potential
> an irq conflict. that is, u may disable the already installed lpt port or
> disable (one of) the port(s) on the new card. the solution to this is to
> buy a more expensive card with multiple printer port addresses.
> there is the potential for damaging printers connected to manual ab
> switches by shorting out something if all the pins in the ab switch dont
> engage or disengage simultaneously. manual ab switches void the warantee
> some printers.
> electronic ab switches dont have any moving parts so they cant short out
> any device (in this case a printer and camera) connected to the switch.
> Thanks to all those who replied.
> [ source:
> Randy Smothers <>,
> "Bill Woodland (Squeek)" <>,
> "Tom Prugh",
> "ucmisdrh",
> Rolf Hemmerling <>,
> "John W.Osborne" <>,
> Jason Williams <>,
> "Kevin McCluskey",
> "Mark L. Bardenwerper, Sr." <>. ]
> Mark Andrew Nassy <>