Serial floppy drives - test-drb@ccmp.vtda.org

4 Sep 2002

...
 From: tlindner(a)ix.netcom.com

  On Wed, 4 Sep 2002, Tony Duell wrote:
  However, the original question mentioned RS232.
Which is _not_ the same
 as serial. RS232 implies certain voltage levels. 
 The CBM and Atari drives do not use an RS232 interface.   
 AND,..
 If I recall correctly, the Tandy Pdd1, although it was "almost
 RS-232" used TTL, NOT RS-232 voltage levels.  There were some trivial
 adapters available to permit it to work with "real" RS-232 signals. 
I always thought that was called RS-422.

The Macintosh standard serial port was a RS-422 serial port. When I went
to look up what that meant, the only difference I could find was the
voltage levels.

RS-422: 0v to 5v
RS-232: -5v to 5v

The documentation I found went on to say that RS-422 was backaward
compatiable with RS-232.

-- 
tim lindner                    tlindner(a)ix.netcom.com

Hi
 No, 422 is not backwards compatible with 232.
RS-422 and RS-485 are both specs for driving differential
lines. RS-232 can be +/- 12 volts but the receiver may
have lower levels ( I forgot what the requirement was ).
 The document was not correct about RS-232/RS-422. It may
be that one could make them work under specific conditions
but these signals are not backward compatible.
Dwight