bio_zwbb@jhunix.HCF.JHU.EDU (Dr. William B. Busa) (11/02/89)
A while back I asked about serial port expanders -- essentially a smart T switch which would connect any of several serial devices to a single serial port on my computer, based on control signals from the computer. Below I briefly summarize the responses; if I've missed any I'm sorry -- our system was off the network for nearly a week. There were three categories of responses: 1. The unhelpful suggestion that I should buy a board with more serial ports and put it in a free slot. I had mentioned in my original posting that this was not feasible. 2. Well-intentioned information about multiplexers, which can be found in most computer supply catalogs (Misco, etc.). No help here, either. These suckers are *expensive* and they waste a lot of time polling the peripherals to see who needs servicing. In my application the computer should call the shots, not the peripherals, and since I'm controlling laboratory equipment the response must be instantaneous. 3. ***THE ANSWER TO MY PRAYERS*** : Exactly the sort of smart T switch I was looking for is sold by Bay Technical Associates, Inc. 200 N. Second St., P.O. Box 387 Bay Saint Louis, Misssissippi (800-523-2702 or 601-467-8231) Their "A Series" of port expanders have one port on the computer side and either 4, 8, 11 or 17 ports on the peripheral side. The computer selects the peripheral it wants to be connected to by sending a CTRL-T followed by a port number; this is trapped by the box while everything else is sent through (other control signals can be specified, and *two* CTRL-T's will send the second one through). The boxes run at up to 9600 baud. Each port's protocol is programmable via PROMs. The 4-port box (Model 524A) costs only $339 (10% discount for education and hospitals). I have not received mine yet, but the specs look promising and the price is right. Bay Tech also sells fancier boxes, which provide large buffers, multiplexing, etc. etc. Along these same lines, I am informed that another manufacturer makes much the same thing: Black Box Corp. (412-746-5565). but I don't know anything more about them. -- Dr. William Busa, Dept. of Biology, The Johns Hopkins University, Charles & 34th Sts., Baltimore, MD 21218 (301) 338-8207 bio_zwbb@jhunix.hcf.jhu.edu uunet!mimsy!jhunix!bio_zwbb