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SDECM Overview


SDECM -- A Brief Overview

by Stuart Baker
Stuart Baker Software
9370 Golondrina Drive
La Mesa, CA 91941-5654
(619) 466-8811

This article describes SDECM, a monitor that has served BIOC and ITAM users well for many years. SDECM is an acronym that stands for the San Diego Environment Control Monitor. It is an extension to the ECM program that is included in the OS/32 Reliance package. It provides the same basic functionality as the original ECM, but it also handles terminal pairs, inbound and outbound dial lines, and supports automatic screen save and disconnect for dial lines.

James Millard of Concurrent Computer Corporation created SDECM. Its initial public release was in June of 1983. Since its original release, many people have contributed to its development. The contributing authors are: Stuart Baker of Stuart Baker Software, Ron Stordahl of Digi-Key Corporation Corporation, Jim Kaiser of the University of Notre Dame and Valerie Griffin of Telos Corporation. SDECM is available through the Interchange library under the number IUG0116. The current revision is R05-11. If anyone is using a version prior to R05-06, I seriously recommend obtaining a new version. Valerie Griffin has fixed many problems that the other authors could not find the time to address. Thank you Valerie for a job well done, SDECM is now a very stable program.

I will now describe several of SDECM's features. When SDECM is started, it assigns the TERMINAL.ECM file. This file contains a list of terminals for SDECM to control. Each line in the file is formatted as follows:


Where: BI01: is the BIOC terminal name, IT01: is an optional ITAM terminal name, and /D|G|L are optional switches that define the line class. SDECM was developed to allow users to access Reliance with its required ITAM driver, and at the same time give MTM users the benefit of the BIOC driver. Has the advent of CTD made SDECM obsolete? No, it definitely has not. Many systems, such as LIMS sites, can benefit from SDECM's handling of terminal pairs. In addition, SDECM's handling of dial lines adds a great deal of flexibility to any system that uses modems.

First let's address the terminal pair issue. Terminal pairs are defined at sysgen time by generating more than one device name to control the same physical device. Before CTD, the drivers generated were a BIOC device for MTM and PASSPORT use, and an ITAM device for Reliance use. Since SDECM does not check the device codes for the devices that it controls, you do not have to specify an ITAM device for the second terminal name. If you use modems, I strongly recommend sticking with BIOC or CTD for your first terminal because SDECM uses the extended connect and disconnect functions to control the modem lines. If you are a LIMS site, using the 241 driver, you can sysgen a BIOC/LIMS terminal pair and use SDECM to access MTM with either driver. From SDECM you type MTM to use the BIOC driver and MTM R to use the LIMS driver.

Now let's look at the switches that control the way SDECM handles each line. For locally connected terminals you typically do not use any switches. SDECM maintains two banner screens, the first screen is used when only one terminal is specified, the second screen is used for terminal pairs. The second screen typically contains codes specific to the 6312 class of terminals and would cause problems on terminals that do not support Reliance. If you are running LIMS software and do not use reliance you can make the two banner screens the same.

The /D switch tells SDECM that a line is a modem used for inbound calls. For this line class, SDECM maintains an OnHook and OffHook status that may be observed with the status command. While waiting for a call, SDECM uses the connect extended option. If you use terminal pairs on your inbound dial lines, each caller is greeted with the message "Thank you for calling, does your terminal support Reliance?". If you are using a 6312 terminal or a terminal emulator like PC-Passport you should respond with a Y. You will than receive a display of the second screen. If you answer with the letter N, you receive a display of the first screen and the REL command is disabled. When you issue the BYE command, the disconnect extended option is used to break the connection.

The /G switch specifies a line is a modem used for both inbound and outbound calls. Inbound calls are handled as if the /D switch was used. The added feature is that the line is getline eligible. This means that programs like PASSPORT can request a line for outbound calling. The getline request has two formats:

  • The generic getline request asks SDECM to choose the first available line from all of the getline eligible lines. SDECM searches from the top of its list to maintain compatibility with rotary or hunting phone lines.
  • The specific getline request asks SDECM to check the availability of the requested line only.

The getline feature is very powerful in that you can use the same phone lines for both inbound and outbound calls. SDECM handles all of the overhead of choosing a line that is not in use.

The /L switch specifies a line is a modem used for both inbound and outbound calls, just like the /G switch. Lines assigned with the /L switch may only be obtained through a specific getline request, not a generic getline request. This option is useful if you have modems that need to be handled in a special manner and you don't want them to be picked up with a generic request.

One of the big advantages of SDECM over ECM and Terminal Switch (TS) is that it has a synchronized sweep time. This allows MTM users to access foreground programs even when they enter MTM from SDECM. The foreground interface must be disabled for the standard ECM because it attempts to pick up MTM terminal based upon a repeated interval. Since this interval is not linked to the closing of a logical unit (LU), the terminal might be picked up immediately after the LU closes. In this case the foreground task can not assign the terminal and you end up at ECM, while MTM is waiting for a response from the foreground task that never comes. This is a very sticky situation because you are still signed on to MTM, and yet you are back at ECM. SDECM on then other hand starts its sweep time when the LU is closed and terminates the sweep when the LU is assigned. Since the sweep delay is synchronized with the LU closing, SDECM does not interfere with the foreground interface. If you wish to use the foreground interface with SDECM, you must change a statement in the MTMSGN.MAC file. This statement grants ECM terminals the privilege to issue foreground commands. Change the ECMFLAG statement to read:


Note that you must not be using the standard ECM or TS if you make this change. Only monitors with synchronized sweep times like SDECM will function properly with this option.

Well that about does it for this issue. Don't you think that it is about time to order your copy of SDECM from the Interchange Library? I am looking forward to seeing everyone at Interchange '91 in Caesar's Palace. Come to our booth and see how impressive the R02 version of PC-Passport is. The flexibility and power of this new version of our 6312 emulator is truly something to behold.

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Article Copyright 1991 Stuart J. Baker

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