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UnderColor, Volume 1, Number 4, February 1, 1985

  • Title: Defusr
  • Author: Terry Kepner
  • Synopsis: Q & A.
  • Page Scans: Link


I own a 16K Extended Basic Color Computer with an F board, which l recently upgraded to 32K.

Fifteen to twenty minutes after the computer is turned on, it will automatically print random characters on the screen and the program in memory is ruined.

When my Dad first got the computer, the problem wouldn't take place until a few hours after the computer was turned on, but the time has been steadily declining.

Recently we removed the RF shield, but that only prolonged the time for about half an hour.

The warranty on the computer has expired, and my Dad doesn’t know any more about the problem than I do. Any suggestions?

Michael A. Stuller

Rolla, MO

Sounds familiar. The first thing I would check is the power supply. Some of these aren’t soldered as well as they should be, and can sometimes cause the problem you mention. Get a soldering iron and, after unplugging the computer, re-solder the parts on the power supply.

Next, if that doesn't cure the complaint, run the computer with the cover removed and wait for it to malfunction. Now carefully touch the top of each of the memory chips and the CPU and SAM chips. One of them should feel much hotter than the rest. That is probably the errant chip. Replacing it should cure the problem. Be careful: running the computer with the cover off is dangerous.

If you can’t find a bad chip, you’ll just have to take the computer into the repair shop.

I own a 64K Extended Basic computer and would like to add disk drives. Forty-track DS-DD drives seem to be best, but can their special controllers read RS-DOS disks? Do they have RS-DOS—like commands?

Also, could a PIA be mapped in the range of $FF60—$FFBF for communication with a parallel printer? What signals would the PIA have to supply and/or accept to work with a parallel printer?

Jeff Allen

Bridgton, ME

You have to contact the individual manufacturers to see if their DOSes can read RS-DOS disks. Some of them have special utilities that will do the job.

As long as you had a parallel device that was hardwired to read the proper addresses, yes, you could drive a parallel printer. Just make sure the addresses you select aren’t being used for another purpose. The voltages would all be TTL. In theory, the parallel device would monitor the printer PIA and wait until it saw data being sent to it. When the PIA is selected for output, the parallel device would scan the Color Computer data bus, read the data, and ship it out to the printer. Ideally, you would want to monitor the printer for ready/not ready status. The technical manual for a parallel printer will give you the pin-outs and uses for the various connections, and you can decide which you want to use.

The PIA’s themselves wouldn’t be used, since

they’re strictly serial device units, and not designed to operate with parallel data.

When I use my four-foot flat cable with my disk

drive interface everything works fine, but when I use the cable with the Multipak Interface, garbage comes on the screen and the keyboard crashes.

The computer is 23K EC with an HJL keyboard


William H. Link

Richfield, NC

The extension cable is the problem. The disk

ROMpak uses fewer control signals from the computer and is less susceptible to interference from other sources. The Multipak Interface has its own power supply and must make all the control lines available to the various ROMpaks. As a result, interference is much more likely. The only cure is to make the connecting cable as short as possible, and to make sure it is a grounding plane cable (that is, that it is wrapped in metal foil that’s grounded to both the computer and the Multipak Interface).

In the July 1984 issue of The Color Computer Magazine, on page 69 appeared the disassembler for the last four parts of ROM. I used my EDTASM to compare Extended Basic ROMs 1.0 and 1.1 (I have two computers here).

Comparing the four lines of source code from $9178#$9117 on both ROMs bore out Jake’s contention that there was a bug in the ROM which has been corrected in the Extended Basic ROM 1.1.

The comparative listings are below:

Ext. Color Basic 1.0 Ext. Color Basic 1.1

9178/ SUBB #0A 9178/ SUBB #0C

917A/ BHS 9177 917A/ BHS 9177

917C/ ADDB #3A 917C/ ADDB #3C

917E/ STD, U++ 917E/ STD, U++ As you can see, $9178 has been changed from 12 to 10. However, running the listing below gave me identical results on both versions of ROM. Am I using EXP(X) the wrong way to yield different results on the different ROMs, or is the error using EXP above nine possible elsewhere?

The listing:

10 FOR X=7 TO 15 STEP .246

20 PRINT"EXP(";X;")=",EXP(X)


The results were identical on both ROMs, with and without using Step.

Dennis Anderson

Brooklyn, NY

The bug is the Print Using command trying to display the proper exponent. In evaluating the exponent for the Print Using format, the original ROM subtracted 12 from the tens digit, instead of 10!

l have developed some programs that employ the RND operator, but have found it is not very random; in fact, it is quite predictable. The following simple program and its output will illustrate:

20 CLS

30 FOR N =1 TO 5

40 X = RND(8)



The output are repeated on runs as follows:

4 3 7 8

3 5 1 8

2 3 5 6

6 1 5 2

4 7 8 6

. . . which looks fine, however, when you shut off the computer and then power up and reload again, the output are exactly the same. Is there a programming technique which will give me truly random sequences?

Richard M. Auclair

Westfield, MA

Microsoft is the culprit. This RND problem is on most computers that use Microsoft Basic. The only true solution is to make your own RND machine code function and include it as part of your programs.

That takes skill and requires a lot of work. The easy kludge solution is to set up an INKEY$ routine at the start of your Basic program that requires the operator to "Press Enter to Continue," with the INKEY$ loop including xx=RND(9). This is best done as part of the title page. Since the amount of time it takes the operator to respond by hitting the Enter key will be random (compared to the speed with which the loop will cycle), you'll get a random starting sequence each time. The only way for the operator to get the same sequence every time would be to hit the Enter key at the exact same instant every time the program starts. Given the computer’s speed and the slowness of the human response time, you are almost guaranteed that will never happen, except as random chance.

I have a 32K Extended Basic Color Computer. I just recently purchased a number 0 disk drive. I am a novice, so I am not too familiar with all the terms used with the computers.

Please tell me how I may get a printed copy from the disk directory displayed on the TV screen. I would like to print it on my DMP-100 printer. I have called several Radio Shack stores and computer centers, but they do not know how to do it.

Lloyd G. Lutey, Sr.

San Jose, CA

That’s an easy one — just type

Poke 111,254:DIR.

Your directory will be sent to the line printer.

I have a 16K Standard Basic Color Computer (gray). This year I plan to upgrade to 64K, get Extended Basic, and add a disk drive. Everything looked fine until Radio Shack discontinued the disk drive. What are my alternatives? I read that the new drive (white case) will not work with my model. Why? When I upgrade Basic will I get the new 1.2 version? (I have the latest model board before they put out the CC II.)

Lewis Todd

Natchez, MS

Don't worry, the new white case drive zero will work just fine with your old gray Color Computer. The confusion about which drives worked with which computers has finally been cleared. The gray case computer can use either the gray or white case disk drive zero. The white case computers can run only the white case disk drive zero. If you have the Multipak Expansion Unit, you can use either the gray or white case drive zeros with either of the color computers, gray or white. `

If you buy a new computer, you’ll get the new Basic 1.2. Otherwise you’ll still have the old version ROM. The ROM version refers to the Standard Basic ROM, not the Extended Basic ROM.

Is there any way my C. Itoh printer will work with my Color Computer (original CoCo, upgraded 64K, Ext., revision board E)? I bought a C. Itoh Model 1550B Dot Matrix Serial Impact Printer. I purchased the printer without finding out how to connect it to my CoCo. I can 't seem to get the proper hook-up or settings on the printer to enable it to run on my computer. It has serial interface, 25-pin connector (RS-232C), seven or eight bit capability. I am using Radio Shack’s serial DIN plug to RS-232C cable end.

Brent Prokopishin

Saskatoon, SK S7J 4G4, Canada

The RS-232 cable sold by Radio Shack is designed only for use with modems, not with printers. You have to either re·wire the R/S cable or make one yourself. In most cases the set-up is easy. If you want to modify the R/S cable, get a pair of pliers and a screwdriver. Take apart the DB-25 connector. You’ll see four wires exposed. One wire goes to Pin 1 of the DIN plus and to Pin 1 of the DB-25. Leave it alone. Take the wire from DIN Pin 2 and check its current position in the DB·25. If it isn’t in position 20, use the pliers to pull the pin out of the DB connector and put it in position 20. DIN Pin 3 should go to DB Pin 7. DIN Pin 4 should goto DB Pin 3.

If you decide to make your own cable, just wire it the way I described above, and you’re ready to go.

Now set the baud of the printer to 600, the word size to eight (seven if you have ROM version 1.0), no parity checking, and two stop bits. That should do the job. Good luck.