Serial Cable Specs

One of the Newton 2.x OS Q&As
Copyright © 1997 Newton, Inc. All Rights Reserved. Newton, Newton Technology, Newton Works, the Newton, Inc. logo, the Newton Technology logo, the Light Bulb logo and MessagePad are trademarks of Newton, Inc. and may be registered in the U.S.A. and other countries. Windows is a registered trademark of Microsoft Corp. All other trademarks and company names are the intellectual property of their respective owners.


For the most recent version of the Q&As on the World Wide Web, check the URL: http://www.newton-inc.com/dev/techinfo/qa/qa.htm
If you've copied this file locally,click here to go to the main Newton Q&A page.
This document was exported on 7/23/97.

Serial Cable Specs (8/9/94)

Q: I want to make my own serial cable. Which wires and which connector pins do I use?

A: To create a hardware flow control capable cable for Mac-to-Newton or Newton-to-Newton communications (also called a "null-modem" cable) all you need are two mini-din-8 connectors and seven wires connected as follows:

Ground (4) -> Ground (4)  (also connect to connectors' shrouds)Transmit+ (6) -> Receive+ (8)Transmit- (3) -> Receive- (5)Receive+ (8) -> Transmit+ (6)Receive- (5) -> Transmit- (3)Data Term Ready (1) -> Clear To Send (2)Clear To Send (2) -> Data Term Ready (1)


You should use twisted pairs for 6/3, 8/5, and 1/2, to improve signal quality and reduce attenuation, especially in long cables. You can use side-by-side pairs, as in telephone hookup cable, for short cable runs.

Remember that because RS-422 uses a differential signal for transmit and receive, you always need two transmit and two receive pairs, and a break of either wire will cause communications in that direction to fail. The advantage, however, is significantly longer and more reliable cable runs than RS-232.

If you don't use hardware flow control, you can eliminate the 1/2 pair, but that's not recommended unless you know this cable will be used only in software flow control situations.

Q: What's the pin mapping on the Newton-to-PC (DIN-to-DB9) cable?

A: Here it is:

Note that the pin numbers shown are as defined above.

PC (DB9)    Newton (DIN)    ========================1           1    2           3    3           5    4           7,2    5           4,8    6           1    7           N/C    8           N/C    9           N/C    N/C=not connected.