mac serial pinouts

From: Lawrence Walker <lgwalker_at_look.ca>
Date: Fri Oct 6 03:01:55 2000

 
> > Hey,
> > Can anyone tell me which pins (and I don't know the numbering
> > scheme, so please include that) are transmit, receive, and gnd on a
> > Mac 8-pin mini-din port?
>
> The pinout I have numbers the pins like this :
>
> o o o
> 8 7 6
> o o o
> 5 4 3
> o o
> 2 1
>
> Looking into the socket.
>
> The pinout is :
> 1 Handshake output
> 2 Handshake (or external clock) input
> 3 Tx Data -
> 4 Ground
> 5 Rx Data -
> 6 Tx Data +
> 7 No Connection
> 8 Rx Data +
>
> For RS232 connections : take transmit data (output from Mac) from
> TxD-. Ignore TxD+. Feed receive data (input to mac) into RxD-. Ground
> RxD+ (link 4 to 8) and link the external device ground to that
> connection as well. Handshake In is like CTS or DSR, handshake out is
> like RTS or DTR
>
> Hope that helps
>
> -tony
>
 A problem exists with Mac cables. Unless you're using the newer
hispeed cable you can't connect to your ISP even tho it seems to
test ok with a terminal program. I ran across this problem in trying
to hook my Mac up. I fussed and fumed over it for about a month
before stumbling across the solution.
 There is nothing to physically indicate any differences between the
2 cables. A little.Practical Peripherals file explains it as follows:

 The Macintosh has too few pins for a full RS-232 implementation.
The RS-23 standard has 25 pins, however, most Mac ports have
only 8 pins. The following pins are needed when talking to a high-
speed modem:

 Input RX
 Output TX
 Clear to Send CTS
 Ready to Send RTS
 Data Terminal Ready DTR
 Carrier Detect DCD
 Ring Detect RI (can be done in software)
 Ground

So if ring detect is covered in the software, you should only need 7
pins to handle communications. Unfortunately, the Mac ports
double as RS-422 ports, and some of the pins are used to support
this. Therefore the Mac only guarantees five or maybe six pins that
can be used. While this wasn't a problem for 2400 bps modems,
since they didn't require RTS/CTS, and even CD was rarely
connected. You could just turn off your modem if it didn't hang up.
This of course didn't work for BBS operators or ARA servers, so a
cable was developed that used the RTS (usually called HSKo on
the Mac) pin for DTR, and the CTS (usually called HSKi) pin for CD.

As you can imagine, this cable configuration is a problem for high-
speed modem users, since the RTS/CTS lines are used for CD and
DTR. You couldn't take advantage of the full potential of your high-
speed modem. That is why a new "standard" hardware handshake
cable layout was developed.

 Here's the pin outs for that cable:

 Function (Mac) Function (RS-232) Pin (Mac) Pin (RS-232)
 Receive data Receive data 5 3
 Send data Send data 3 2
 Ground Ground 4 & 8 7
 HSKi CTS 2 5
 HSKo RTS & DTR 1 4 & 20
 GPi CD 7 8

Unfortunately, not all Macs support Pin 7 (GPi) thus leaving us with
keeping CD on at all times. Also, since DTR is tied to RTS a high-
speed modem must be set to ignore any change in DTR.
Otherwise an RTS flow control change would cause the modem to
hang up the telephone line. If both your Macintosh and your
hardware handshake cable support Pin 7, then you could properly
track changes in DCD, but setting the modem to track DTR will still
cause the modem to hang up when RTS is toggled. END

Perhaps this is the problem Marion is wrestling with.

ciao larry


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lgwalker_at_look.ca
Received on Fri Oct 06 2000 - 03:01:55 BST