Right where to begin.....

VIA Port B assignments

Bit Used as
7 DAV in from IEEE
6 NRFD in from IEEE
5 Retrace in from video (used for sensing when to write video RAM)
4 Tape#2 Motor control (on/off)
3 Tape data out (write line used by BOTH Tape#1 and Tape#2)
2 ATN out to IEEE
1 NRFD out to IEEE
0 ...

Hi Mats,

I dug out my copies of Raeto West's "Programming the PET/CBM" and "PET and the IEEE-488 Interface" and re-read the relevant sections to give you more definitive information about what system activities use the 6522 and to what extent. Hopefully I should be able to get this info posted this ...

Hi Mats,

When looking at the internals of the PET/CBM one should always remember that you are effectively looking at software written 26+ years ago when systems were much more closed and proprietry than now. Plus, as you rightly mention, hardware cost an awful lot more (32K of RAM cost an arm and a ...

Hi Mats,

That's great if you're finding the CBM system software isn't stamping on your code as you've written it.

A few things to watch (if you've not came across them already), and definitely to be avoided in the middle of a data transfer are :

- cassette I/O, this alters the IRQ vector and ...

This big problem trying to use IRQs on the "user port" on CBM/PETs is the fact that the system's 60Hz IRQ tramples over so much and twiddles bits in just about all the I/O chips (both 6520s and the 6522 doing clock updates, keyboard scanning and buffer processing, tape drive switch sensing/motor ...

Doing "classic" 6522 hardware handshaking on CBM/PET machines is a bit of a nightmare as you have this mismatch of control lines. Namely PA0-7, CA1 and CB2 as the "user port". PB0-7, CA2 and CB1 are used for a variaty of system functions including the 2nd cassette interface, upper/lower case ...

Those two books are "PET/CBM Personal Computer Guide - Adam Osborne and Others - Osborne McGraw Hill" and "Programming the PET/CBM - Raeto Colin West - COMPUTE! books".

I've still got the Raeto West book but went and gave the other one away about 8 years ago when I had to rehome my PET collection.

Ah that it explains it....

The first edition of the PET manual could best be described as a "great work of fiction lightly spinkled with a few facts". At the time Commodore were a legend in the industry for the attrociousness of their manuals. Much of what appeared in the early manuals was, for ...

Hi Mats,

It's exactly the same monitor as was shipped in the "new ROM" (BASIC 3.0) PETs. On the "old" ROM PET (BASIC 2.0) you had to load it from tape. There have been 3rd party monitors that may have used a different command syntax but TIM's has never changed.

TIM does have access to the IEEE ...

The syntax for the TIM save command is :

s "name",device,start,end

So it would be :

S "NAME",02,0400,076D

In addition remember that cassette #2 is the edge connector on the right hand side. The one on the back is cassette #1.

Microtan did something similar on their 6502/6809 SBC board using a 74S288 BiPolar PROM. Bags of flexibitily, a bit of a bugger trying to work what combination of PROM data and link settings were needed for a given memory map. And the CPU clock circuit was very fussy about which make of 74LS04 it ...

Hi Garth,

It puzzled me as well not finding any mention of it in the MOS hardware manual (it's labelled Frist Edition, August 1975) as I was fully expecting to find it. Other data sheets I looked at last night (Rockwell, CMD) state that RESET disables IRQ in the CPU and I've always written code on ...

Hi Ruud,

To quote the original MOS 65xx Hardware Manual :

"It should be assumed that any time the RESET line has been pulled LOW and then HIGH, the internal states of the machine are unknown and all registers must be re-initialised during the restart sequence".

When dealing with IRQ it states ...

That reminds me - must get back to building the desk clock for my friend. Should be nice as it's going to be using an Noritake-Itron GU256x128E-3900 VFD graphic display module.

Been playing around with it to get used to the command structure using their MODMAST software and connecting it to a PC ...

I think you should post the exact text of the question as your second attempt at explaining it made less sense than the first.

For instance why mention a 4x4 keypad if there's only 1 button connected?
If the button (or even the entire keypad) is connected to Port B, how can you expect to read it ...