Minor Tektronix success story.

From: Philip.Belben_at_powertech.co.uk <(Philip.Belben_at_powertech.co.uk)>
Date: Mon Aug 17 14:14:47 1998

A minor success story compared with some I read here, but I wanted to
share it with you...

This weekend I finally got my Tektronix 4052 graphics computer loading
and saving on a Commodore 8050 disk drive. The problems:

Commodore's weird handling of IEEE-488 protocol, especially with OPEN
and CLOSE. This requires bit 7 (the 128s bit) to be set when sending a
secondary address; bit 4 - usually the 16s bit of the address - tells
the drive whether it's an open or a close.

This was easily solved - the Tektronix WBYTE statement gives full
control over such things.

But the Tek is designed as a tape based machine. You FIND a file on the
tape and type OLD to load it. The machine then resets and loads the
program.

On a disk, you WBYTE _at_40,240: some bytes to specify the file name. But
if you type OLD _at_8,0: it asserts IFC during the reset, thus causing the
drive to have forgotten all about your program by the time it comes to
load it...

So I toyed with the idea of cutting the IFC line in a suitable cable.
But then I came across the APPEND statement. "APPEND _at_I/O address:line
number" loads a program without resetting, renumbering it to start at
the specified line. Neat.

So I now have a program to display the directory of the disk, prompt you
for a filename and APPEND the file on the end of itself. It then
performs an INIT (initialise variables, IFC and things) and drops into
the program.

Saving is easier, so less automated. You type something like
WBYTE _at_40,241:48,58,80,82,79,71,82,65,77,32,78,65,77,69,-13
WBYTE _at_63:
SAVE _at_8,1
WBYTE _at_40,225,63:

Not perfect, but it works. If anyone has an 8050 at the VCF, I'll
happily demonstrate!

Now, has anyone got a PET hard drive? And, for that matter, has anyone
got a MUPET system for sale?

Philip.
Received on Mon Aug 17 1998 - 14:14:47 BST