21 Nov
2009
21 Nov
'09
8:22 a.m.
----------------------------------------
Date: Fri, 20 Nov 2009 09:54:04 -0600
From: csquared3 at tx.rr.com
To:
Subject: Re: BIT 483 / was Re: Non-fake Apple 1 on ebay
Brent Hilpert wrote:
That link is quite interesting, especially the pictures. From the way
the front panel is laid out, I would assume values are stated in octal
rather than hex. The bits on the panel seem to have a 2-3-3 pattern so
hex FF would be thought of as octal 377. This appears to be true of the
2 address bytes as well. I think this means that for example address
hex FFFF would be represented as 377,377. That would take some real
mental gymnastics to deal with if one was entering a short program or
debugging manually. Maybe you can stay under 000,377 for short programs
and avoid that problem. Not having read any of the docs I don't know if
that is possible.
My old Microdata 820 has a 4-4-4-4 front panel pattern which is rather
easier to deal with I think. Of course you realize this discussion has
me wanting to drag it out of the garage and get it going again. :)
Later,
Charlie C.
Hi
The splitting of the octal address is called split octal.
Heathkit did this on there H8/89. Of course it makes more
sense on a 8 bit processor. It even makes sense to use
octal for the 8080 type of instruction codes.
On the BIT 483, it had some sense because of what they
call page size. It was only 256 bytes.
As I think Chuck mentioned, this limited the size of
the variable length arithmatic. The only time while
programming one uses an address greater than 377o is
indirect addressing. This means that it makes sense
to split it rather than have a complete full octal
address.
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A fellow
on the VCForum found a BIT 483. Now that is
at least as rare as the A1. I have a Nicolet 1080 that I only know
of 5 total. There may be more but they are not likely in
another collectors hands without them contacting me or Sellam.
I was going to ask about the BIT 483, but I see you and Chuck are already on
top of it:
http://www.vintage-computer.com/vcforum/showthread.php?p=120353
I love hearing about these little-known machines. Wish there was picture of the
internals. Anybody know what sort of market these things found?, or more about
the company origins/destiny?