Classic Computer Magazine Archive CREATIVE COMPUTING VOL. 9, NO. 3 / MARCH 1983 / PAGE 132

Getting serious with the color computer. (evaluation) John Steiner.

Getting Serious With The Color Computer

The TRS-80 Color Computer has been a part of my life for over a year. I started a project to write a book, and after spending a few long hours in front of the typewriter, I realized a word processor for my computer would be nice.

One of the necessary accessories would be a disk drive. Cassette program files have their place, but for a project as large as text files, a disk system is indispensable.

The current choice is between Radio Shack's disk system and the Exatron disk operating system. I chose the Radio Shack system for two reasons: it should be compatible with future Tandy software releases, and the DOS is in ROM.

Tandy has provided an excellent operating system for the Basic programmer who doesn't want to learn to use a disk operating system. The 35-track double density system is completely transparent to the programmer. No "system' or special DOS handling is required to operate the system. Even though I am a novice programmer, I was able, using the Disk System manual, to write and use a Basic word processor.

Another advantage of the ROM-based DOS is that no space is taken either on the disk or in RAM for DOS. The only disk space not available for user files is track 17, the disk directory. Only 2K of overhead is required for disk buffers, and this can be reduced using the FILES command.

As a result, you can have a disk operating system on a machine with only 16K of memory. Before upgrading my machine to 32K, I felt only slightly handicapped by having to relinquish the 2K for the disk buffer.

Disk user file capacity is 156,672 bytes, and a maximum of 68 files can reside on a single side, of a soft-sectored 5 1/4 disk. The files are catalogued in TRSDOS fashion, with an 8-byte file name and 3-byte extension.

The drive 0 package includes a single drive unit, a ROM disk controller pack, drive connecting cable, and an instruction/programming manual. Another drive can be added to the system if required, and an optional four-drive cable allows interfacing of up to four drive units. One requirement of the disk system is that your Color Computer have Extended Color Basic.

A single drive unit has been in operation on my Color Computer for about six months, and has operated almost flawlessly. The only problem I have noted concerns television interference. There is a notice included with the unit that warns of television interference when you are using the drive on an early model computer. My computer, serial number 337, certainly qualifies. I was, therefore, not surprised to notice interference on my home television when I used the drive. I have not noticed any interference on my monitor. Tandy offers to modify any computer that requires correction of the problem. I have never felt it was severe enough to have corrected. Besides, I couldn't bear to be without the computer for the few days that the modification would take.

Since the drive unit has gone out of warranty, I have had only a couple of minor problems. Occasionally the DOS would not initialize properly, and either the computer would be locked up or Basic would work but disk Basic commands would only bring a response of ?SN ERROR. I traced the trouble to dirty contacts on the ROM pack where it plugs into the Color Computer, and used a pencil eraser to clean the contacts.

The only other problem I have had occurred when the drive unit would respond only with I/O errors. I tried LOAD, SAVE, and DIR, and all gave the same error message. Since the unit was out of warranty, and since I have had some experience with electronics, I used a phillips screwdriver to remove the drive from its case.

The problem turned out to be quite simple. The drive belt had simply slipped off the flywheel. After reinstalling the belt, the drive again performed flawlessly. I don't know why it slipped off, and it hasn't happened again in nearly two months.

First, The Bad News

As you can probably tell, I have no real complaints with the drive, however as with all equipment, there are a few things that I dislike. Included in this list are the following. Utilities seem to lack sophistication. As an example, BACKUP requires a formatted disk, unlike Model I and III TRSDOS which formats during the backup process. BACKUP also copies all bytes on a disk, whether it contains only one small file or a full disk. For disks with little information on them it is easier to load and resave those files.

COPY will transfer files from one disk to another, but it requires at least two drives. File access protection routines are lacking. There is no lock or password protection capacity. The only file protection is the write-protect tab.

Another feature I would like is autostart, or DO files. There is no way to provide a turnkey system as the drive is now equipped. Though variables cannot be transferred from one program to another easily, it is possible to load and run a program from inside another program. My last gripe is the lack of an ON ERROR GOTO statement.

The Good News

There, I got all my gripes off my chest; now for some good news. First, the cost. Though the $599 price on the disk system itself seems high and is comparable to prices for other disk systems (e.g., Atari, Apple), total system price is very competitive. A TRS-80 Color Computer disk system with 32K, and a single drive can be purchased for under $1200 from many suppliers. Compare that to Atari and Apple with the same capacity.

The user manual is written to the same high standards as the two Basic programming manuals. Even though I was completely unfamiliar with file handling on a disk system, I was able to learn as the manual took me step-by-step through sequential and direct access files. I found, to my surprise, that my cassette file programs were transferred to disk with little problem.

Listed below are two file command lines, the upper line creates a text file on cassette; the lower line does the same on disk.

1000 OPEN "1', #-1,


1000 OPEN "1', #1,


As you can see, the only difference is in the buffer number. this buffer number specifies which file is to be used. To transfer cassette file programs to a sequential disk file, use the line editor to remove the minus signs in the disk statements. Up to 15 disk buffers can be open at the same time. These details are best left to the disk manual.

Another handy command you can use is POKE &HFF40,0. With this command, you can turn off the drive motor. Normally this is not required, as DOS does this for you.

I wrote a simple program to transfer disk files to tape for tape backup purposes. One problem with it was that the drive continued to run during the tape write procedure. This is because opening a tape file causes program control to leave DOS and enter the cassette file write routine. DOS doesn't get a chance to shut off the drive. Never use this command while a file is still open. In other words, the command must be preceded by a CLOSE command.

The manual includes several sample programs that can be used. The list includes a membership file, checkbook and budget programs among others.

A service manual is available for those hobbyists who are technically oriented. There is a wealth of practical material on preventive maintenance, as well as service and repair information. Maintenance is straightforward; however you run the risk of voiding the warranty should you open the drive unit during the warranty period.

For example, drive speed adjustment is easy. My drive has strobe bars on the flywheel. To adjust for proper speed, insert a disk and use DIR to start the motor turning. Use a small insulated handle screwdriver to adjust the motor speed control while viewing the strobe bars under a fluorescent light. When the row of bars marked 60 Hz looks stationary, the drive is adjusted properly.

When I compare the Color Computer with other home computer systems, I an impressed with the TRS-80 cost/feature ratio. It provides many features and capabilities that are unheard of on systems that cost twice as much. The Color Computer, coupled with the disk system is sure to make large inroads in the home computer market. I have found over the last year that the system is vastly underrated, and has far greater capacity than most people give it credit for.

Products: TRS color computer disk drive(Computer apparatus) - Evaluation