80-Bus News

Missing Star

My system is a Nascom 1 with 64K RAM & Microsoft (ROM) basic interpreter. I have recently found something funny and I don’t have any explanation about a M.S.S. (Missing Star Screen) phenomenum. This little program will show you the problem:

10 CLS
20 FOR  Y=1 to 15
30 FOR  X=1 to 48
40 SCREEN X, Y
50 PRINT "*";
60 NEXT X, Y
70 GOTO 10

This program is self explanatory but it does not work !

Philippe Wetterwald, France

(Ed. – It is all to do with the SCREEN command not resetting BASICs counter for the number of characters in a line, so every so often BASIC says ‘Ah, time for a line feed.’ Try setting WIDTH 255 to disable line feeds.)

ROM/​RAM ZEAP, TAPES & DISKS

On page 28 of INMC80 issue 3 Mr. C. Bowden is having some problems with running ROM ZEAP in RAM.

This is cured by replacing the contents of location D5F0 (which normally contains the code INC (HL) with a hex 00 (code for NOP). This disables the memory ‘test’ routine which arranges for ZEAP to crash when run in RAM.

Of course, you may not like printing the above but I think that anyone with the infinite intelligence required to get CP/M running should be able to work it out in no more than 15 minutes.

On page 8 of INMC80 issue 4 Mr. R.S. Marshall writes about poor quality recording tapes. I feel that the problem is basically two-fold: the so-called ‘computer’ tapes (i.e. C12 long etc) are of lower quality than practically any common audio tapes. Certainly their mechanics are very poor and the only good reason for using them (rather than audio tapes) is their lower price – if they work.

The other reason is that the data density at (say) 1200 baud is not far from 1 bit/0.001″ and most commonly used (i.e. cheap) cassette recorders do not have their head azimuth adjusted to this degree of accuracy. If (as is often the case) the tape is recorded on one machine and replayed on another, then unless the heads of the two machines are identically set-up to within 0.0005″ or better (over the tape width) the data will be unreadable. This particular problem can be eliminated by replaying the tape (which was probably recorded in stereo with the same data on both channels) on a stereo deck and only connecting one channel.

I myself have been using TDK D-C60 & D-C90 tapes for about two years and on average get about one error per several hours (yes) of playback time, at 1200 baud. The deck is a Pioneer CT-200, costing about 85.00.

Regarding David Parkinson’s “1.5 Mbaud” article on page 41 (INMC80-4) I would be very interested to hear more about his 8″ Nascom disk system, particularly how he wrote his BIOS. Also, does he still have working versions of MOVCPM.COM and SYSGEN.COM? It seems to me that as soon as the BIOS is modified (for 8″ drives) then the standard MOVCPM cannot any longer relocate the CP/M package for different system sizes. Also, which format did he chose?