joels@tekred.UUCP (03/04/87)
I am having a problem with the Amiga RS232 port. I am trying to use it to talk to an X10 powerhouse. The Amiga can hear the X10, but the X10 cannot hear the Amiga. The Tek 834 DCA I'm using for debugging can hear both, and the X10 can hear the 834. I put a scope on the transmit line from the Amiga to measure the voltage levels. I found the positive swings to go to about 12-15 volts but the negative only to minus 1.25-1.5 volts. This is not within the RS232 specs. It does work with other devices such as the Hayes modem though. I also tried the program on Wendy's Amiga (I didn't check the voltage levels) and the results are the same. Is this problem generic to the Amiga, or do we both have a hardware problem? Any ideas for a fix? Joel Swank Tektronix, Redmond, Oregon
grr@cbmvax.cbm.UUCP (George Robbins) (03/06/87)
In article <1028@tekred.TEK.COM> joels@tekred.TEK.COM (Joel Swank) writes: > > I am having a problem with the Amiga RS232 port. I am trying to use >it to talk to an X10 powerhouse. The Amiga can hear the X10, but the >X10 cannot hear the Amiga. The Tek 834 DCA I'm using for debugging can >hear both, and the X10 can hear the 834. I put a scope on the transmit >line from the Amiga to measure the voltage levels. I found the positive >swings to go to about 12-15 volts but the negative only to minus >1.25-1.5 volts. This is not within the RS232 specs. It does work with >other devices such as the Hayes modem though. I also tried the program >on Wendy's Amiga (I didn't check the voltage levels) and the results >are the same. Is this problem generic to the Amiga, or do we both have >a hardware problem? Any ideas for a fix? > >Joel Swank Tektronix, Redmond, Oregon The voltage should swing between about +12 and -5 volts, perhaps a volt less depending on the loading. From the numbers you mention, it sounds like the BSR device has a heavy pullup resistor to something like +15 volts and/or a diode clamping the input to ground. Most likely the BSR thing is non-standard, violating the 2K input impedance called out by the RS232 spec, although it probably works ok with devices having a +12, -12 swing. One solution is to find the offensive input circuitry in the BSR thing and improve it, the other would be to try slipping the following little circuit into the connector shell: o pin 23 (+12) | \ / 4.7K resistor | |-----/\-------o wire that was on pin 2 (tx data) / 220 resistor pin 2 |< o----------------| 2N3906 (pnp general purpose) |\ \ | o pin 14 (-5) -- George Robbins - now working for, uucp: {ihnp4|seismo|rutgers}!cbmvax!grr but no way officially representing arpa: cbmvax!grr@seismo.css.GOV Commodore, Engineering Department fone: 215-431-9255 (only by moonlite)
upl@puff.WISC.EDU (Future Unix Gurus) (03/06/87)
In article <1028@tekred.TEK.COM> joels@tekred.TEK.COM (Joel Swank) writes: > > I am having a problem with the Amiga RS232 port. I am trying to use >it to talk to an X10 powerhouse. The Amiga can hear the X10, but the >X10 cannot hear the Amiga. > >Joel Swank >Tektronix, Redmond, Oregon The problem cannot be generic, as I have written BASIC code to access my x10 powerhouse, and it works fine through the internal serial port. I understand a number of Amigae went out with a bad chip in their serial ports (another symptom of this is that they blow easy), maybe your machines are of this vintage? Thats the only possibilty I can think of (all though it also may ne a problem in your x10... have you tried hooking it to an IBMPC and running it with the included software?). I can send you my (unfinished) basic code if you would like to see it. I abandoned basic when my TDI Modula II came, and have been so busy with real programming for school that I haven't been able to get back to it. Jeff Kesselman Temporary Adress: ihnp4!uwvax!puff!upl Real Home: ihnp4!uwvax!puff!upl!uhura!captain (The real home is preferrable, but won't be back up for another week or so)