piclist 1995\12\01\121524a >
Thread: Macintosh Serial Interface?
face BY : David Tait email (remove spam text)

Ben Kwok-Yiu Li wrote:

> Do Mac's have the same RS232 or is it the RS422 or something completely
> different?

I answered a similar question on the Microchip BBS a few month's back.
Here is roughly what I said then:

If your Mac is the same as my old Mac SE then it's not exactly RS232 (I
think it's RS422 or somesuch) but can be made to interwork with RS232.
The connections are via a Mini-8 connector:

   8 7 6         8 RXD+   7 GPi   6 TXD+
  5  4  3        5 RXD-   4 GND   3 TXD-
    2 1             2 HSKi    1 HSKo

GPi  is a general purpose input (don't ask me what it's for).
HSKi is Handshake in.
HSKo is Handshake out.

To connect a 3-wire RS232 cable to the Mac:

    RS232              MAC
    -----              ---
     RXD               TXD-
     TXD               RXD-
     GND               GND RXD+ (i.e. RXD+ is wired to GND.)

I usually resolve the ambiguity about which pin is which by using a
DVM to find TXD+ or TXD- as they will be at +/-12V unlike RXD+ or RXD-
which will be around 1V or so.


In reply to: <199512010723.HAA02228@listserv.rl.ac.uk> from "Ben Kwok-Yiu Li" at Nov 30, 95 11:19:09 pm
See also: www.piclist.com/techref/io/serials.htm?key=serial
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