Doctor Dark’s Diary – Episode the Tenth!
A little thing for Nas-Sys 3 users.
Scenario: a Nascom user (not you, though, because you only use your
Nascom for serious purposes, of course) has just typed in the whole 4K of
Space Invaders, only to find that it won’t run. It must be a typing error.
Now, if he had had T2, T4, or even Nas-Sys 1, the whole thing could have been
typed in using the L command, and lines with errors in them would have been
rejected by the monitor. So, for Nas-Sys 3, here is a fairly minimal program
to generate checksums from a program in memory. Comparing these with the
listing will allow the easy discovery of typing errors.
To use it, you would just type the Hex code into an unused bit of RAM,
and execute it with the following instruction: Exxxx yyyyNL, where xxxx is the
address of its first byte, and yyyy is the address of the first byte of the
program you wish to check. The checksum for the first eight bytes will be
printed. Press the space bar to produce each subsequent one. Press any other
key to exit from the program. When you do this, the address of the start of
the line just checked is printed.
I was originally going to put a listing of the program in, but it
would have taken up a lot of space, besides which, programs to do this are in
all the glossies [Computing Today, anyway] so the Nas-Sys 3 users will all
have written their own by now.
Another Nas-Sys 3 fix.
Bits and P.C.’s have kindly told me how to change their BASIC
programmers’ toolkit so that it will work with Nas-Sys 3. All you have to do
is change the byte at B185 from 08 to 0C, and they say all will once again be
sweetness and light. I have not tried it, but I bet they have! Just goes to
show, if you write and ask your friendly dealer a question, they will let you
have all sorts of valuable information. I suppose we had best not overdo it,
or they will not have enough time left to sell Nascoms in...
I have edited out an incredible [but completely true] story, which was
here, about a different Nascom dealer who lied to me on the phone, since it
could have been a mistake on their part.
*** INTERLUDE *** [Cue potter’s wheel, etc.]
While you watched the soothing picture of a man making a jug on a 78
rpm record player, I got me a Nascom 2 with a disk drive and CP/M. The latter
is a lovely thing to have, with some reservations about the standard CP/M
issue assembler and editor provided: the assembler is only capable of 8080
code, using weird mnemonics [Intel], and the editor, whilst being powerful in
many ways, seems to think a teletype is the only form of input and output in
use. By this I mean that you can’t move the cursor up the screen to some other
line and work there, or step back to the middle of a line and amend it. But...