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Using Model 4 JCL files

Take advantage of the power of TRSDOS 6.0

Model 4 Al Mashburn

So you have this new Model 4 computer that comes with a neat new operating system that does everything but tie your shoe? The only problem is that some of the features are complicated and every time you want to use them, you have to go look it up in the manual so you can enter the commands one-by-one until you get the function you want. An example would be the Memdisk. First you have to enter "system (drive=2,driver="memdisk")". Then questions about which bank, what density, and if you want it formatted are asked. Now, most of the time, the answers are going to be the same, so why should you go through this when you want to use Memdisk, the Comm program, or any other program that requires setup? That's what you got the computer for. Let it do the work.

You may not have realized it, but when you bought your Model 4 disk system, it came with two languages. There is a BASIC interpreter, but there is also a Job Control Language. JCL was designed to run the computer when a pre-determined set of keyboard inputs was needed. Let me say this right now. The JCL that comes with the Model 4 can do a lot more than I'm going to show you here. It is a powerful tool that can literally save hundreds of man (or woman) hours. I am just going to scratch the surface and hopefully whet your appetite. As long as I'm sidetracked, run (don't walk) down to your computer center and get a copy of TRSDOS 6.1 or 6.0.1. The numbers aren't important, but it is necessary that you have the updated DOS. If you bought your machine 38 Basic Computing after September, 1983 you probably already have it. The updates include fixes in the way some JCL jobs are done.

There are three programs I run which require some input to get them set up. The first is BASIC. That is pretty easy to remember, but I always forget to specify one file for maximum memory. I go into BASIC, then remember that I forgot (F=l) again, exit BASIC and reenter the right way. As I mentioned, Memdisk is another program that goes through setup as does Comm. So, I wrapped up all three into what I call SHELL/JCL. A shell is a program that sort of insulates you from the operating system. It is really nice if someone who is a little computer shy has to use the machine.

There are no linenumbers in JCL, so it's a little hard to follow the program flow in large jobs. It might be a good idea to study the owner's manual if one of the terms or commands seems confusing.

The first line of Shell is a comment line. It just so happens that we want a comment line at the start of the job to list the options, but even if we didn't need a comment, all JCL programs should start with a comment because some won't even run without it. All comment lines start with a period.

The second line uses JCL command Keyin. Keyin allows input of a number from 0 to 9 and works like the BASIC INKEY function. That is, you don't have to press enter after selecting a number. The slashes (//) before Keyin are the way JCL tells between its own commands and those it is issuing to the computer. Think of Keyin as

Listing 1 - Shell/JCL

//KEYIN YOUR CHOICE

SYSTEM (DRIVE=2,DRIVER= "MEMDISK" ) D D Y

SET *CL OOM/DVR (B=300,W=8#S=l,P=OFF) COMM *CL //STOP-///

.EXITING TO DOS //EXIT

JCL files

BASlC's "On X GOTO." When you key in a choice, the program searches through the job by looking at the //# blocks. In other words, if you were to enter 3> it would search past //l and //2 until it got to //3. Then it would execute the commands after //3. In this case, it would issue the commands necessary to go into the Comm program. You will note that there are no leading periods or slashes in the commands after the //#. When the program comes to one of these lines it is just like you typed them in from the keyboard.

At the end of each block (//l, //2, etc.) there is another JCL command. In Shell it is either //EXIT or //STOP. These tell the computer what to do when it has done the job. //STOP means to stop the job and hand control over to the program you are in. In other words, if you are in BASIC when the job is done, you will be left in BASIC. Sometimes this isn't good. In the Memdisk job, if you //STOP at the end, you are left hanging with no TRSDOS Ready or anything, so we //EXIT. //EXIT

returns us to the TRSDOS Ready prompt no matter where we are when the job is done. Do not use //EXIT unless that's where you want to be. If you use it in a job like block //3, you would enter the Comm program and then exit back to TRSDOS. That's like building a boat in your house then tearing it apart to get it outside. You're right back where you started.

Near the end of the program you'll see three slashes (///); these mean "there are no more blocks past here." If you were to enter 8 at //Keyin, the program would search past block //3 and come to ///. The program would stop looking for block //8 and would execute the command following /// (in this case, //EXIT to TRSDOS). The D,D,Y in block 2 are the answers you must give to set up Memdisk for a 128K machine. If you have a 64K, you will have to change it.

If you do have a job that you would like to do with this program, or you want to change some of the commands in this one, you will need some way to enter the JCL program

(it is not entered from BASIC). The operating system comes with the Build command to enter JCL programs. The syntax to enter this program would be BUILD SHELL/JCL. Build has no editing features so if you made a mistake (some of us do) you would have to "Remove" the program and retype it. When you Build a program, there cannot be a program with that name on the disk. The best way to make small changes is to use a word processor that can save text in ASCII form. In Scripsit, you would SAVE SHELL/JCL,A. To run this program, enter it as shown using Build. Then enter DO=SHELL/ JCL. The reason for the = is that there is no compiling needed so the = tells the computer to execute without compiling. Once you are satisfied that the job works as you want it to, go to TRSDOS ready and type AUTO DO=SHELL/JCL. Then press reset and when the computer boots it will run Shell. This will save you a lot of time so you can go out and make a lot of money and buy more computer equipment.

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