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Article #188Re: q:RS232 on a CBM64
From: Chris Blum
Date: Fri, 17 Mar 1995 00:47
Date: Fri, 17 Mar 1995 00:47
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2633 bytes
On Thu, 16 Mar 1995 11:59:20 GMT, Rob Janssen (rob@pe1chl.ampr.org) wrote in <D5J7yy.1o7@pe1chl.ampr.org>: > In <3k6mn2$c0@chris.telip.uni-sb.de> chris@chris.telip.uni-sb.de (Chris Blum) writes: > >So what do you think the MAX232 contains? Or the 1488/89 chips in > >your PC? :-) > They not only invert, but also convert between TTL levels and the RS232 > standard, which specifies positive and negative voltages to be used. > Using only an inverter will result in marginal levels, it may work or > may not work. It _will_ work with 1489s on the PC side (virtually every serial port has them), because they're designed to behave that way. Using a MAX232 at the CBM64 end would be a very clean solution, admittedly, but any simple inverter (with overvoltage protection) will do as a quick hack. I've used one NPN transistor and two resistors for each direction (with an additional diode shorting negative voltages from the PC at the base of one of the transistors to ground) in those good old days of youth; so much for level conversion. Chris -- Chris Blum <chris@phil.uni-sb.de> http://www.phil.uni-sb.de/~chris/
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