had rather a nice surprise, because I’d swapped over the wiring to the two
keys, so now the “ENTER” key was by itself on the end. The only trouble was
that I’d lost the key cap for it, and jabbing at the thin stalk of plastic was
even more difficult than hitting the key in its original place. I searched
everywhere, but no sign of, the button (I always seem to lose things when I’m
drunk. I once lost my false teeth, I think I must have flushed them down the
loo after I’d been sick.) (Keep it clean please – Ed.) So a trip was made to
my local friendly electronic parts shop, who had only red double width caps.
Bliss! I now have a big distinctive key that I can’t miss even if I try. See
diagram 2 for details of how to change the printed wiring on the back of the
keyboard.. (If you’re using a G805 with SYS, why not change the keyboard table?
SKEWING THE SKEW.
I have the use of another CP/M machine besides my Nascom. This is an
AVL Eagle, and also uses 18 sectors per track, but with a different skew.
Problem? How do I transfer programs from one computer to the other.
Ensure that the system on all disks is of the same size, with source
disks containing a CP/M system from the computer that’s being copied from, and
the receiving disks containing the other system. Log in the source disk, and
load the program without running it, as described above. Put in the receiving
disk, and do a ^C to change the BDOS in memory... this doesn’t alter the BIOS,
so now save the program onto the new disk, with the new format. Simple isn’t
it (provided that you remembered how long the program was, and didn’t have to
go back and use STAT, and then start again!). And it works, no matter how many
sectors there are per track, the only requirement being that both types of
disk should work in the same drive.
Write a special program to do the job using direct calls to the BDOS
primitive functions, or simpler, adapt somebody elses’ program. Practical
Computing published a fast disk copy program by T. D. Lee in their Sept ’81
issue, which uses a skew table to speed things up. By having separate tables
for reading and writing, the skew can be changed on an entire disk very
quickly indeed. For your information, the skew table can be found at 311AH in
a 16K system, 119AH in a file created by MOVCPM, and 121AH in MOVCPM itself.
The number of sectors is at 313AH, 11BAH, and 123AH respectively.
COMMENTS IN SUBMIT FILES
So you’ve got a submit file, but you can’t remember exactly what it
does..... Just put in comments as you would in any source file. CP/M will
ignore anything from a semicolon(;) up to a carriage return. It will also
ignore anything after most terminators (:, \, etc), but Digital Research don’t
promise to support anything other than a semicolon in future releases.
FAKE CALLS TO WBOOT
While on the subject of undocumented features of CP/M, on page 16 of
INMC80/2 David Hunt wonders whether making fake calls to WBOOT in order locate
the jump vector table, so as to make direct calls to the I/O drivers, is
legal. Sorry Dave but it ain’t. However, John Pierce of Digital Research has
stated that since everybody uses it, they will try to support it in future
releases, but it may not be possible, so they will continue to not document
how to find the jump vector table.
CP/M 1.4 contains two undocumented function codes that are documented
in version 2 onwards. These are used to set (28) and monitor(29) the read only
status of disk drives.