22 Jul
1997
22 Jul
'97
11:25 a.m.
I have some comments on the PET FAQ, but I've lost Larry Anderson's
e-mail address. Accordingly I am posting it here, with apologies to all
who don't wish to read it.
WHAT MODELS OF THE PET ARE THERE?
The PET line was Commodore's first computer line after purchasing MOS
Technologies the primary design of the computer (as well as its
microprocessor, the 6502) was by Chuck Peddle. The line was labeled in
series' the first series, the 2001 series, the european 3000 series, and the
modern 4000 and 8000 series, and the final single unit 9000 series which is
the SuperPET.
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
have also heard that the 8200 series runs BASIC 4.5, but mine runs 4.0.
[...]
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.
- 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.
- Later versions had 4.0 ROMs installed
Was this not only available as an upgrade?
> 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
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.
- 4.0 ROMs
- molded plastic top
12" displays - updated video controller (prone to
the 'killer poke')
- internal piezo speaker, audible startup, and right margin sound.
- 4.0 ROMs
PET/CBM 40xx (PET= N keyboard/ROM, CBM= B keyboard/ROM, xx= RAM)
- 40 x 25 display, upgradable to 80 columns
- lower case availabe by CHR$(14) which also changes line spacing.
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.
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...
[...]
At this point you must mention the 8296 and 8296D!
[... SUPERPET ...]
MOTHERBOARD SERIES
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
The righthand motherboard was the 2000B and some of the 3000 - the tape ports
were swapped on the 2000N and other 3000 AFAIK.
4000/8000 series (12" CRT)
IEEE user tape #1
+------####-####--##-+
! # # tape
! # # #2
! R exp bus # !
! A #! 2000 Series
! M 9 #! circa 1977/78 Max RAM - 8k
! A #! [daughterboard exp to 32k]
! M R B !
! E O C ! 3000 & 4000 Series
! M M D ! circa 1979/80 Max RAM - 32k
! O S E !
! R F ! 4000 & 8000 Series
! Y ! circa 1981 Max RAM - 32k*
! spkr! [daughterboard exp to 96k]
+--------------------+
8200 series: Again this basic format, but rearranged so the separate keyboard
mod is sensible. 128k RAM on motherboard of which 96k usable (?).
WHAT ARE THE DIFFERENCES AND/OR BUGS OF MY VERSION OF
BASIC?
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. Peeking and poking in upper memory
(thresholds vary!) were disabled to stop people looking at the ROMS. 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"
error.
[...]
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.
[...]
HOW DO I ACCESS THE PET's M/L MONITOR?
The 'timy machine language monitor' (known as TIM to some) is available on all
PETs but the original ROM version. TIM is invoked by executing a BRK
instruction by SYSing any memory location containing a zero (0), most people
enter SYS 1024, as it almost always contains a 0.
TIM stood for Terminal Interface Monitor, according to my manual.
[...]
WHAT IS THE 'KILLER POKE' AND SHOULD I WORRY
ABOUT IT?
This is THE POKE of computer lore, the command that WILL physically break a >
computer! Of course other commands and methods are known that can
potentially cause damage (usually to disks, hard
drives or other mechanical
units), but this is the most notable mainly because it was a command somewhat
commonly used and it affects solid-state circuitry.
History of 'the killer poke'
[ 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
other).
[...]
IF PEEK(50000) THEN POKE 59458,PEEK(59458)OR 32
NO!!!!!! Peek(50000) will only be zero on the original old ROM pets!
CAN I HOOK UP AN EXTERNAL MONITOR TO MY PET?
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
work.
[...]
<><><><><><><><><><><><><><>
Philip Belben
<><><><><><><><><><><><><><>
Bloedem Volke unverstaendlich treiben wir des Lebens Spiel.
Grade das, was unabwendlich fruchtet unserm Spott als Ziel.
Magst es Kinder-Rache nennen an des Daseins tiefem Ernst;
Wirst das Leben besser kennen, wenn du uns verstehen lernst.
Poem by Christian Morgenstern - Message by Philip.Belben(a)powertech.co.uk