uhclem@trsvax.UUCP (07/28/87)
<Software can fix any problem introduced by hardware. - Old Director of Hardware Proverb> >/* Written 2:04 am Jul 23, 1987 by kksys.UUCP!gk*/ >A friend has been attempting to use a Tandy DMP120 printer which he scavenged >off his old TRS-80 on an IBM-AT clone which is running UNIX --> It is not >happy. The printer runs ok on the TRS-80, and runs on -some- IBM clones >with MS-DOS (depends on dos release). The local Radio Shack service center >says the old printers are not compatable with the IBM-type machines >(including Tandy systems), and suggests the purchase of a new printer. >More woes.... One of the silliest printers ever made. The guys in Japan must have laughed for weeks over this one. The basic problem of the 120 is that it insists that everything be perfect. In particular, if the print strobe exceeds some amount that is slightly over the Centronics 1.5usec strobe spec, the printer decides that something is wrong and halts the built-in CPU. You have to cycle printer power to get it out of this. Because strobe is active-low logic, if you turn the printer on BEFORE you turn the computer on (at least on Model II, 16, 6000, III, 4 and 4P units I tried), the printer "sees" a strobe signal exceeding the defined length and commits hari-kari. So much for the "turn your peripherals on first" statement. You either had to cycle power on the printer once the computer was on, turn them both on at once (50-50) or turn the printer on last. One of the numerous problems with IBM-PC-family computers, apart from the fact that they don't show up in mirrors, is that the print strobe, that 1.5usec pulse, is generated by software. A 1-shot to handle this would have cost .22, but Nooooo!!!! And IBM, for some god-unknown reason, put the circuitry on there to allow software to read the last character sent to the printer! Right! I write software all the time that forgets what it just told the printer to do! Someone find out what a 74LS244 is worth! More that .22 I'll bet! Of course, there is no problem if you write software for a particular machine running at a certain speed, but to date there are AT and AT-clones out there that run at 6+1w, 6+0w, 6.77+0w, 8+1w, 8+0w, 10+0w, 12+2w, 12+1w, 12+0w, 16+3w, 16+2w, 16+1w, 16+0w, plus another dozen I haven't heard of or "know nothing" about. Now, did Microport (or whoever) write the code to handle that timing regardless of what speed machine you happened to boot on? If not, then you will have the problems you are having. Other problems from mis-sized print strobes on some printers include double-characters, or the printer ignoring the strobe entirely and just sitting there. The cure is to change the values for the strobe generation. Call the vendor in question and ask them for a patch address. Then try tuning it yourself if they don't have a ready fix for you. Another way out might be to use one of these printer buffers that are available. Some of these things pay no attention to the duration of the print strobe (within reason) on incoming data and generate reasonable strobes for the printer. That might hide the faulty signals from your printer so it will work. I think I tried using the Tandy buffer with a Terminet once and it didn't handle it. Ended up with double-characters. Feeding the buffer from a machine with a hardware-generated strobe worked fine. <This information is provided by an individual and is not nor should be construed as being provided by Radio Shack or Tandy Corp. Radio Shack/Tandy Corp has no obligation to support the information provided in any way. But I'm not a potted plant! That's why I am not in Washington!> "Thank you, Uh Clem." Frank Durda IV @ <trsvax!uhclem> ...decvax!microsoft!trsvax!uhclem ...convex!infoswx!hal6000!trsvax!uhclem "If everybody's somebody, then things are getting boring."