To:         all federal users at federal
From:       Strang
Subject:    STU III data cable information
Date sent:  07/06/89 4:17 PM
Attachment  Title: STU III data port cable spec
             Kind: Text


I have gotten enough requests for STU III serial data cable information that I composed the attached data sheet with information on building and buying these cables.  GRiD does not stock, supply, or support these cables.  The customer needs to make or buy them on their own.

The East Coast Resource Center has one pair of STU III serial data cables for demo use.  These cables have 25 pin female (DB-25S) connectors on the computer end, and there are 9 to 25 pin adapters with them, so they can be used with PC or PC/AT style serial ports.  To use them with GRiD 19 pin serial ports, GRiD model 6100 cables (19 to 25 pin) will be needed.  Only one of these STU III data cables is shielded for Tempest use; the other cable and the 9 to 25 pin adapters are not shielded for Tempest use.

A few notes on STU IIIs and their data modes.

1) STU IIIs will not go into data mode or remote mode at all unless the RTS input on their data interface is asserted (true).  Once a STU III is in remote mode, it will not obey Hayes style modem commands unless RTS is asserted (true).

2) When in data mode or remote mode, STU IIIs will not go off hook unless the DTR input on their data interface is asserted (true), and they will go on hook if DTR becomes unasserted (false).

3) STU IIIs will obey Hayes Smartmodem style commands only in remote mode.  The AT&T STU IIIs that we have had a chance to use have a very inaccurate imitation of the Hayes style modem command set, and I suspect that other STU IIIs are just as bad.  This implementation is bad enough that most programs that use Hayes style modem commands will not work properly with STU IIIs.

The gist of this discussion is that STU IIIs are NOT plug and play with many pieces of data communication software.  They can be made to work predictably and reliably, but you have to deal with the STU IIIs particular requirements.

Will