Re: Unidentified subject!

[Frank Sergeant <FS07675@xxxxxxx>]

Tuesday, December 27, 1994

>>
>>Does this mean, that no 12V-5V converters are required? Can I just 
>>connect IN0 to TD, OUT0 to RD, and Gnd to SG? 

>Yes. I have done it directly on several computers.  I tried it
>But it appears PCs (8088-486) machines that I use have
>no problem with 0-6V on a serial line.

  I, too, have had good success using 0 and 5 volt levels to connect
to the serial port of PCs (zero volts in place of the -3 to -15 the
PC expects; 5 volts in place of the +3 to +15 the PC expects).  When
running from the serial port of a 68HC11, I typically run each signal
through a CMOS inverter  (74HC4049, for example).  If you have direct
software control of the bits, you can do the inversion in software.
I do use current limiting resistors, just on "general principles."

  I was bit, once, on this with some old serial cards that insisted
on a negative voltage and just would not accept zero volts.  I've
never had any trouble on newer machines, as far as I know.  Besides,
I hate to spend the power the MAX232 chip requires.

  -- Frank

   Frank Sergeant
   fs07675@academia.swt.edu