CLASSICCMP digest 122

From: Larry Anderson & Diane Hare <>
Date: Wed Jul 23 22:59:44 1997

Subject: PET FAQ

> What about the 8200 Series? I am not sure of the differences between this, the
> 8000 series and the 500/700 (B/P) series - see my post earlier this week.

I don't have ANY information on the 8200 series, I suspect that it was
not widely released (or not at all) in the U.S. The 500/700 series are
not in the PET line, those are the B-series machines and would be a
separate FAQ - IMO.

>> Large Keyboard PETs (no more internal datasette drive):
>> PET 2001 xN (x=8,16,or 32 depending on amount or RAM it was shipped with)
>> - Full-size key keyboard w/PET graphic symbols imprinted on keys
> I dispute this. The 2001 xN, of which we had several at school, had the new
> ROMs, the new motherboard (using 2332 ROM chips) but the small keyboard and the
> built in C2N. This was the essential difference between the N and B machines.

Have to disagree with you on this one, the 'calaulator keyboard' PETs
seem to have the designation on 2001-8k or 2001-8/c (c referring to
calculator keyboard). The N designation meant [N]on Business and
[B]usiness style keyboards, both full-size, can find many sales ads and
books to refer to on that one (though if I were running a business on a
PET, I would have preferred the keyboard with the most keys...)

>> - Upgrade ROMs
>> - Many steel cased, some w/molded plastic tops.
>> - many with clearer green on black displays
>I thought all the N and B machines had green screens - we even had one straight
>2001 (old ROM) with a green screen.

I think Commodore still had extras in stock (also small yeyboards &
tops), the blue screens aren't common but tere are some in later models
(kinda like finding VIC-20 keyboards in C-64 units)

>> - Later versions had 4.0 ROMs installed
> Was this not only available as an upgrade?
I am going by personal experience here, there were 8" diaply PETs sold
with 4.0, I saw a couple come through our school.

>> PET 2001 xB (labeled as CBM, Commodore Business Machine)
>> - Full size xx key keyboard (no graphics symbols printed on keys)
>> - Upgrade ROMs (powers up in upper/lower case mode)
>> - Later versions had 4.0 ROMs installed
>> - Many w/molded plastic tops some steel cased.
> Our green-screened old-ROM machine was labelled CBM, but was again a small
> keyboard/internal tape machine. Otherwise I remember little about the B
> machines

Hmmm, I have yet to see such an animal... But as I mentioned a few
answers back, with Commodore's thriftyness anything was possible. :)

>> PET/CBM 40xx Series (PET= N keyboard/ROM, CBM= B keyboard/ROM, xx= RAM)
> I wasn't aware of a small keyboard 4000 series. Interesting.
Again, N does not mean small keyboard.

>> 80 column series (can be set to 40 column mode via software.)
>Can it?!? I wasn't aware of this. You can restrict the area in which it prints
>on the screen to an arbitrary rectangle, but it doesn't behave like the
>40-column machines in that the screen is still physically 80-column, it doesn't
>handle wrapped text, etc.

On many of the Commodore P.D. disks there is a program called 4032.C (I
think there is a .C on it...) it will bump your 8000 into a 40 columns
to run the 40 column programs on the disk.

> The 8200 series could be set from 80 to 40 columns by unsoldering and moving two
> chips. I haven't done this to mine yet...
Never heard of 'moving' chips, I read it was one of the ROMs (the one
that supplies the startup values...) that determined 40 or 80 column (as
well as video RAM memory too.) I guess you mean replacing two chips,
then yes. Going back to 40 is a bit easier since you don't have to add
RAM like in the 4000 PETs.

> At this point you must mention the 8296 and 8296D!
I'll have to dig up some solid info on this, as 'I said it is pretty
uncommon here.

>[... SUPERPET ...]
Got one, still puzzles me, also how much space I should devote to it as
I have only seen one (the one I bought recently). Will probably add
more as I get more time and information not very many people have asked
about them.

>> 2000 series(9" CRT) 3000 & 4000 series (8" CRT)
>> IEEE user tape #2 IEEE user tape #1
>> +------####-####--##-+ +------####-####--##-+
>> ! # ! #!
>> ! # ! #!
>> ! # exp ! #! exp
>> ! # bus ! ROMS #! bus
>> ! # ! F E D C A B 9 #!
>> ! # ! #!
>> ! ! ! !
>> ! ! ! !
>> ! ROMS ! ! !
>> ! F E D C A B 9 ! ! !
>> ! ! ! !
>>tape # RAM MEMORY ! tape # RAM MEMORY !
>> #1 # ! #2 # !
>> +--------------------+ +--------------------+
>The left hand board is a hybrid of the original motherboard (of which there were
>no fewer than _four_ versions). Remember the original motherboard used 2
>kilobyte (800 Hex) ROM chips (6540s in most, 2316s in some). The ROMS were
>therefore not F E D C A B 9 but F8 F0 E D8 D0 C8 C0
'Programming the PET/CBM' gave me those diagrams and you are right about
the ROM sizes... Will have to re-do that one.

>The righthand motherboard was the 2000B and some of the 3000 - the tape ports
>were swapped on the 2000N and other 3000 AFAIK.

Will keep with Programming PET/CBMs numbering for now, I'm trying to
answer questions not confuse people more... They should suffice all my
machines except the original (of course) have the tape #2 on the inside.

> 8200 series: Again this basic format, but rearranged so the separate keyboard
> mod is sensible. 128k RAM on motherboard of which 96k usable (?).
Again I have no data on the 8200 PET/CBMs, point me toward your FAQ on
it... *grin*

>> Original ROMs
>> Commodore had not yet implemented the IEEE-488 disk routines. Arrays are
>> limited to 256 elements due to a bug in firmware. There is no machine
>> language monitor nor could the PEEK command access locations above memory
>> location 49152. The upper/lower case character set was inverted (SHIFT for
>> lower case) (note: reading my sources there are ALOT of bugs, will take a
>> while to compile them)

>Some of these were not bugs but features. [so Microsoft would have Commodore believe...]
>Peeking and poking in upper memory (thresholds vary!) were disabled to stop people
>looking at the ROMS. [Common among early micros fortunately Commodore learend the
> 'closed box means no 3rd party support' lesson early]
>In the E page are some I/O addresses, so it is re-enabled from there upwards...
>The only other genuine bugs I came across on my own machine (my first ever
>computer was a PET - original ROMs, 13th birthday present in 1980) were one in
>screen editing, and the machine crashes instead of giving the "too many files"

Just skimmed a bit about bugs with the Cassette routines. There was
some usage problems on the PEEKs warning not to cluster them too close
together... Facinating stuff...

>> Added screen 'window' formatting control characters.
>Only in 8000 series and fat 40, AFAIK. The small screen 4000 series did not
>have the new screen controller or many of the new graphics features.
I think you're right on that... still have to research that one more.

>> The 'timy machine language monitor' (known as TIM to some)...
>TIM stood for Terminal Interface Monitor, according to my manual.

Jim butterfield referred to it as Tiny Monitor in the First Book of
VIC, thanks for the clarification.

>[ Explanation with one or too inaccuracies has been snipped ]

>The old "video controller" could not be put into a faster or a slower mode. It
>was discrete TTL, and simply read the screen memory, shoved it through the
>character ROM, and sent it to the monitor. It would not have affected printing
>speed even if you had speeded it up.

>The old PETs were slow because the SOFTWARE of the print character routine
>waited for the interval between screen scans before updating the screen memory.
>This reduced conflicts over the screen RAM which would have resulted in random
>pixels (snow) being illuminated on the screen. There was an input on one of the
>I/O chips which was hooked up to the video circuitry and told the routine when
>to access the video RAM.

>The famous poke was actually to another register of the I/O chip, and configured
>this input as an output. The older pets didn't mind (much!), and the print
>character routine saw the screen as always available, but on the later ones with
>the new video controller, this conflicted with another output and caused the
>video controller chip to do a wobbly (and could even have burnt out one or the

Will re-work that one, thanks for the description.

>> IF PEEK(50000) THEN POKE 59458,PEEK(59458)OR 32
>NO!!!!!! Peek(50000) will only be zero on the original old ROM pets!
Hmmm I know that program works on the big screen units... more

>> With the help of the following circuit you can get a composite singnal from
>> the user port...
>> Insert Video Diagram here....
>Don't use the one published in "The PET Revealed" by Nick Hampshire. It doesn't

DANG! It was such a neat plan too! Guess I'll have to forget that
question for now (until I can find an alternative diagram.)

                Larry Anderson
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Received on Wed Jul 23 1997 - 22:59:44 BST

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