Brian's Mac Serial Port Summary    [last revised: 12 September 1996]

The newest revision of this document is always available as a link from URL
http://www.cs.wisc.edu/~tuc/mac/

Send corrections to: tuc@cs.wisc.edu
==============================================================================
Part0:  Legal Mumbo-Jumbo

This document (c)1996 by Brian Cole (tuc@cs.wisc.edu).  The information
contained herein is believed to be accurate but is not guaranteed.  Use
at your own risk.

Archive sites may maintain a copy of this Summary so long as they allow
free access from any site worldwide (no domain restrictions, no reverse
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In any case, this document must remain in its original mono-spaced ASCII
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==============================================================================
Part 1:  Connector Pinouts
--------------------------

First, here are the pinouts.  These are for male connectors, the pins are
pointing towards your eyes.  Female connectors are mirror images of these.

  miniDIN-8           DB-25
    ,----v----.       ,----------------------------------------------------.
   /           \      \ 01  02  03  04  05  06  07  08  09  10  11  12  13 /
  |  6   7   8  |      \  14  15  16  17  18  19  20  21  22  23  24  25  /
  |             |       `------------------------------------------------'
  | 3   4     5 |
  |             |     DE-9
  |_   1   2   _|     ,---------------------.
    |         |       \  1   2   3   4   5  /
    `--.___,--'        \   6   7   8   9   /
                        `-----------------'

                                 ibm       apple(early macs and LaserWriters)
   pin#     DIN-8     DB-25      DE-9      DE-9
  ------    ------    ------    ------    ------
  shield     gnd       gnd       gnd       gnd
      1      HSKo      gnd       DCD       gnd
      2     *HSKi      TD        RD        +5v
      3      TxD-      RD        TD        SG
      4      SG        RTS       DTR       TxD+
      5      RxD-      CTS       SG        TxD-
      6      TxD+      DSR       DSR       +12v(HSKo)
      7      GPi       SG        RTS      *HSKi(DSR)
      8     *RxD+      DCD       CTS      *RxD+
      9                +dcv      RI        RxD-
     10                -dcv (DC test voltage) [DCE->DTE]
     11                QM
     12                (S)DCD
     13                (S)CTS
     14                (S)TD, NS, [fault on IW1]
     15                TC [DCE->DTE]
     16                (S)RD, DCT
     17                RC
     18                DCR
     19                (S)RTS
     20                DTR
     21                SQ
     22                RI
     23                data rate selector
     24                (TC) [DTE->DCE]
     25                busy
      G  +5v (between pins 4 and 5; GeoPort only)

  *HSKi can also be used for External Clock
  *ground RxD+ to SG to emulate RS232 (leave TxD+ floating)

============================================================================
Part 2:  Useful Cables
----------------------

RTS/CTS control flow cable  (DCE device must be set to ignore drops in DTR.)

             Din-8           DB-25 (DCE)
  -----------------          ------------------
  HSKo       1        ---->  4, 20     RTS, DTR
  HSKi       2       <----   5         CTS
  TxD-       3        ---->  2         TD
  SG, RxD+   4, 8     ----   7         SG
  RxD-       5       <----   3         RD
  GPi        7       <----   8         DCD
  gnd        shield   ----   shield    gnd


Null modem cable
  [note:  some DTE devices may need RTS and DTR swapped on the DB-25 side.]

             Din-8           DB-25 (DTE)
  -----------------          ------------------
  HSKo       1        ---->   5        CTS
  HSKi       2       <----    4        RTS
  TxD-       3        ---->   3        RD
  SG, RxD+   4, 8     ----    7        SG
  RxD-       5       <----    2        TD
  GPi        7       <---[   20, 8, 6  DTR, DCD, DSR (DTR holds DCD&DSR high)
  gnd        shield   ----   shield    gnd


The classic "Mac to ImageWriter I" cable

             Din-8           DB-25 (DTE)
  -----------------          ------------------
  HSKo       1        ---->   8, 6     DCD, DSR
  HSKi       2       <----   20        DTR
  TxD-       3        ---->   3        RD
  SG, RxD+   4, 8     ----    7        SG
  RxD-       5       <----    2        TD
  GPi        7       <----   14        (paper out or other fault)
  gnd        shield   ----   shield    gnd


============================================================================
Part 3:  Signals
----------------

What do these things stand for?


  SG      signal ground
  gnd     safety ground

  HSKo    handshake out
  HSKi    handshake in
  TxD     transmit data
  RxD     receive data
  GPi     general purpose input

  TD      transmit data
  RD      receive data
  RTS     request to send
  CTS     clear to send
  DSR     data set ready
  DCD     data carrier detect
  DTR     data terminal ready
  RI      ring indicator
  SQ      signal quality detect
  (S)TD   sec. transmit data
  (S)RD   sec. receive data
  (S)DCD  sec. data carrier detect
  (S)CTS  sec. clear to send
  (S)RTS  sec. request to send
  RC      receiver clock
  TC      transmitter clock
  (TC)    ext. transmitter clock

  NS      new sync                    (Bell 208A)
  DCT     divided clock, transmitter  (Bell 208A)
  QM      equalizer mode              (Bell 208A)
  DCR     divided clock, receiver     (Bell 208A)

============================================================================
Part 4:  Unuseful Cables
------------------------

Note:  This is for my own reference.  Nobody but me should care about these.


Beige cable with "BusinessLand" in red letters.
  RxD+ is not tied to SG but is left floating, so the signals may be
  weak for CS-232.  Also, while HSKi is tied to CTS, RTS is left floating,
  so this cable is "download only".

             Din-8           DB-25 (DCE)
  -----------------          ------------------
  HSKo       1        ---->  20        DTR
  HSKi       2       <----    5        CTS
  TxD-       3        ---->   2        TD
  SG         4        ----    7        SG
  RxD-       5       <----    3        RD
  gnd        shield   ----   shield    gnd


Grey cable, unmarked, with round (not squared) DIN-8 connector.
  The signal ground is tied to the safety ground--odd, but probably ok
  in practice.  HSKi is tied to both CTS and DCD--it seems to me that
  the mac won't be able to see either CTS or DCD drop because the other
  will still be high.

             Din-8           DB-25 [DCE]
  -----------------          ------------------
  HSKo       1        ---->  20        DTR
  HSKi       2       <----    5, 8     CTS, DCD
  TxD-       3        ---->   2        TD
  SG, RxD+   4, 8     ----    1, 7     gnd, SG
  RxD-       5       <----    3        RD
  gnd        shield   ----   shield    gnd


From the American bargain bin
  HSKo is not connected.  The signal ground is tied to the safety ground.

             Din-8           DB-25 [DTE]
  -----------------          ------------------
  HSKo       1        ---->            nc
  HSKi       2       <----   20        DTR
  TxD-       3        ---->   3        RD
  SG, RxD+   4, 8     ----    1, 7     gnd, SG
  RxD-       5       <----    2        TD
  gnd        shield   ----   shield    gnd


============================================================================
end
---
