Closed ROM 2364 substitute: EPROM 27HC641

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27HC641 EPROM,if specifically programmed, are pin compatible with 2364 ROM.

27HC641a.JPG

This Eprom can replace the old Commodore 8K ROM in VIC20, C64, SX64, 1541, many game cartridges,ecc....
A lot of Commodore computers, drivers, cartridges use the 2364 ROM!

The only differences between 2364 and 27HC641 are 3 address pins swapped, consequently it have to be programmed through a converter-socket (into pic) OR it has to be programmed with a manipulated ".BIN" file that exchange the address pins.

Normally this device is NOT programmable with a cheap universal programmer,
so I can program it (correctly) for you.

Price (without PPfees and sending):
7€/pc 9€/pc
(ask for programming service)
Minimum order: 2PCs

Also on sale elsewhere.

27HC641B2.JPG 27HC641B3.JPG
 
Last edited:
8K ROMs implementations

8K ROMs implementations

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 make 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 socket: 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...).


Do you have some others ideas? write on this thread!
 
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yes, of course.
Sending up 50gr to UK will cost: 8.80€ tracked, 2,70€ untracked
 
Hi, I need a kernal for my sx64, can you program Kernal ROM to directly fit into the socket?
I'm from Italy.
Please let me know.
 
Hi, please verify that the device 27HC641 can be programmed by your programmer!
If OK I can manipulate your .BIN file to use it without any adapter during the programming process

Shipment to Austria (max 250gr) is 12,70€ tracked or 5,70€ untracked
 
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