Hi,
I am new to this forum, and as a former user of a Vic20, wanted to share a trick we elaborated to perform such "backups". Bear with me if it's old news, but I think it is fairly creative and new.
It does involve some hardware:
- An 8K static RAM extension. By that time I made a hand wrapped memory extension based on 8Kx4bits memory chips.
- A special expansion board, with one ore more straight slot, and a special last one:
- It had a switch to permute 2 address lines
- It had a R/W switch to allow or forbid modifications
- It had a reset button wired.
The backup procedure was as follows:
- Plug the cartridge in the special slot and swith the address lines. The ROM will not appear at its usual address, the Vic won't boot on the cartridge.
- Copy ROM to RAM extension.
- using the special syntax of SAVE for binaries and specified range of memory to save image of RAM to tape.
The restore procedure was as follows:
- Plug the RAM extension in th especial slot with permuted address line.
- R/W switch set to W
- Use special LOAD syntax for binaries and specified address range.
- Switch R/W to R/O making RAM appear as ROM
- Switch address line back to straight mapping.
- Hit the reset button
- Play
The boot process tries first to read the cartridge location first bytes, then tries to rewrite them. If the write fails and the read returns the expected bytes, the boot process jumps to the entry of the cartridge code.
Hope this may inspire some project,
J-P
Backup on tape of cartridges
Moderator: Moderators
Welcome to the forum. While we don't exactly execute things in the way you describe, the knowledge about having RAM in block 5 is well spread by now. Anyone who owns a 32K expansion or even a fully switchable 8/16K one can share the fruits of cartridge dumps.
I'm not sure if the VIC really tries to write to the cartridge area at boot. I know it reads it for a CBM signature and then will execute any code it finds there.
As for cartridge games trying to overwrite themselves, several of those have been patched over the years to minimize the need of a R/W switch. I won't say eliminate since there may be other uses of the switch.
You don't happen to have some old dumps from your previous VIC times? While perhaps 99% of all known cartridges seem to have been dumped and archived for FTP access, there still appears to exist a few not yet located in modern times.
I'm not sure if the VIC really tries to write to the cartridge area at boot. I know it reads it for a CBM signature and then will execute any code it finds there.
As for cartridge games trying to overwrite themselves, several of those have been patched over the years to minimize the need of a R/W switch. I won't say eliminate since there may be other uses of the switch.
You don't happen to have some old dumps from your previous VIC times? While perhaps 99% of all known cartridges seem to have been dumped and archived for FTP access, there still appears to exist a few not yet located in modern times.
Anders Carlsson
-
Mike
- Herr VC
- Posts: 4845
- Joined: Wed Dec 01, 2004 1:57 pm
- Location: Munich, Germany
- Occupation: electrical engineer
You can use a switchable cartridge expander, which acts upon the BLK select lines. It is not necessary to permute the address lines.
As the VIC only checks during the reset routine, whether the A0CBM signature is present, you can prevent the autobooting by:
- switch off the cartridge BLK select lines,
- power on the VIC
- switch on the BLK select lines.
Then you can save the cartridge data right from the correct address.
To play the backup in a RAM cartridge, that one must be switched on instead on the same BLK range(s), the backup LOADed into RAM, and a reset performed.
Disabling write operations is only necessary for some cartridges, which use the write to cartridge space as copy protection (if it was writable, it can't be ROM, thus is must be a copy).
Anyway, take a look around, there are some interesting hardware projects around here.
Greetings,
Michael
As the VIC only checks during the reset routine, whether the A0CBM signature is present, you can prevent the autobooting by:
- switch off the cartridge BLK select lines,
- power on the VIC
- switch on the BLK select lines.
Then you can save the cartridge data right from the correct address.
To play the backup in a RAM cartridge, that one must be switched on instead on the same BLK range(s), the backup LOADed into RAM, and a reset performed.
Disabling write operations is only necessary for some cartridges, which use the write to cartridge space as copy protection (if it was writable, it can't be ROM, thus is must be a copy).
Anyway, take a look around, there are some interesting hardware projects around here.
Greetings,
Michael
Hi Mike, and carlsson,
Thank you for welcoming me.
I am afraid the tapes were lost is one of the many house moves that happened in over 20 years.
I did have a few interesting things, I remember a super fast arcade game named Matrix, and I also wrote some funny things in Basic like a 6502 disassembler ported from the Apple II (call -151) ROM
I had the 2 Vic manuals, including the thick one with all the ROM entries.
I am afraid all this is just good memories.
J-P
Thank you for welcoming me.
I am afraid the tapes were lost is one of the many house moves that happened in over 20 years.
I did have a few interesting things, I remember a super fast arcade game named Matrix, and I also wrote some funny things in Basic like a 6502 disassembler ported from the Apple II (call -151) ROM
I had the 2 Vic manuals, including the thick one with all the ROM entries.
I am afraid all this is just good memories.
J-P
-
Mike
- Herr VC
- Posts: 4845
- Joined: Wed Dec 01, 2004 1:57 pm
- Location: Munich, Germany
- Occupation: electrical engineer
Not necessarily.oldVic wrote:[...]I remember a super fast arcade game named Matrix[...] I am afraid all this is just good memories.
Do you mean Matrix by Jeff Minter?Michael
Mike,
Thanks, I realise there is a lot of resources out there
And I even found the pdf of the scan of the Programmer's Guide with all the "Kernal"'s addresses... http://www.classiccmp.org/cini/pdf/Comm ... 0Guide.pdf
Cheers,
J-P
Thanks, I realise there is a lot of resources out there
And I even found the pdf of the scan of the Programmer's Guide with all the "Kernal"'s addresses... http://www.classiccmp.org/cini/pdf/Comm ... 0Guide.pdf
Cheers,
J-P