Brian's Mac Serial Port Summary [last revised: 24 April 1996]
"The newest revision of this document is always available as a link from URL"
http://www.inxpress.net/~bcole/mac/ [Alas, the link is broken as of September 2000.]
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
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Summary may not be sold or reprinted without explicit permission from
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In any case, this document must remain in its original mono-spaced ASCII
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translaton (.rtf, .etx, .html), or other alteration is allowed.
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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 ----> 20 DTR
HSKi 2 <---- 8, 6 DCD, DSR
TxD- 3 ----> 3 RD
SG, RxD+ 4, 8 ---- 7 SG
RxD- 5 <---- 2 TD
GPi 7 <---- ? (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.
Very strange, and very dangerous. RxD+ is _not_ tied to SG but is left
floating, so this cable is unlikely to be useful in any way. Also, while
HSKi is tied to CTS, RTS is left floating, so this cable is "upload only".
Din-8 DB-25
----------------- ------------------
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 DCD drop because CTS will still be high.
Din-8 DB-25
----------------- ------------------
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
The data lines are configured for mac-to-DTE, but the handshake line
is typical of mac-to-DCE. HSKo is not connected.
Din-8 DB-25
----------------- ------------------
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
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