I can program 27HC641 like pin compatible 2364..... but what's possible to do with this ROM?
- Spare parts ROMs
Obviously they can replace every ROMs 2364: kernal/basic/games for VIC20 and C64, but also the 4k character generator for C64 (NOT for VIC20..), the ROMs inside the drive 1541, ecc...
- New ROM
for replacing old one: it's possible to program 27HC641 with a specific version of kernal (VIC20, 1541...) or with an modified: for example a new game or software on an old cartridge pcb.
I did a kernal (PAL) VIC20 that at startup, if "commodore" key is pressed, ignore the cartridge presence ..... ecc...
The ROM 24pin socket can be a simple link to bus and will be simple....
- getting a double kernal:
the 2 ROMs will be soldered one on top of the other, every pin but not the 20th, both pins number 20 have to remain not connected, they have to be connected via 2 resistors to Vcc (pin24) for pull-up and connected at the 2 sides of a 2 position switch, the central pin of the switch has to be connected at pin 20 of the sochet: the switch will select the kernal that you want.
- getting a 8K extra software:
a new ROM can be soldered (each pin but not the 20th) on top of basic or kernal ROM, put a pull-up resistor from pin 20 and pin 24 (Vcc), then cut the pin "13" on cartridge connector (/BLK5) and put another pull-up resistor at pin 13 (cartridge side), now solder those 2 pull-upped pins at sides of switch and solder the central pin of the switch at cartridge connector pin 13 MOTHERBOARD SIDE (pin 10 of UC5) and now the BLK5 can be chosen between external standard access or an internal software (without bus collision!)
- getting one or more extra software in a particular space:
a new ROM can be soldered (each pin but not the 20th) on top of basic or kernal ROM, with a pull-up resistor from pin 20 and pin 24 (Vcc).
Example: put 3 diodes with catodes on cartridge connector pin 14,15,16 and anodes soldered toghether into a node that will be called "/3kRAM", put 2 diodes with catodes on pin 9,7 of UC6 and anodes soldered toghether into a node that will be called "/IO2,3".
Now get a switch ON-OFF-ON (with central position that will be off for both sides) and put the ROM pin 20 at central pin of the switch and at the sides put the node "/3kRAM" and "/IO2,3".
Now: with switch in central position the extra SW will be deselected, on position "/IO2,3" will appear 2K ROM from $9800 (example: SJLoad for disk, RABBIT for tape, or else...), on other position "/RAM1,2,3" will appear 3K ROM from $400 (EasyLoad+, or else....).
If you are interested I can program the ROM with the image that you supply to me (remember that I make only the programming service: you remain the only responsable for eventual software copyright/royalty/licence/ecc...).
I sell here: http://sleepingelephant.com/ipw-web/bulletin/bb/viewtopic.php?f=3&t=8320
Do you have some others ideas? write on this thread!
Modding and Technical Issues
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