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EB ROMboard
By Edwin Blink


The Jupiter Ace’s Forth program (operating system) is 8K in size and is stored into two 4K 2532 EPROMS. When you are assembling an Ace like I did or just need some replacements ROMs then turning to alternative 4K EPROM’s like the 2732 is not an option unless you are willing to make modifications to the Jupiter Ace. I prefer not do such drastic measures, cutting tracks and damage the PCB so I had a go on finding a more friendly solution and the EB ROMboard was born (Thank you Steve for naming the board). The board is a small PCB that contains a 8K, 16K or even a 64K EPROM and will fit into both IC sockets simultaneously and the best part is that no modifications need to the Ace’s PCB. After saying that I'm sure you want to know how it works so I won't keep you waiting any longer.

  The EPROM is connected to all the pins in the first ROM socket and also to the chip select pin of the 2nd ROM socket. Both chip selects are combined together with a 1K resistor and a diode to form a single chip select for the new ROM and the chip select from the first socket is also used as an extra address line to select the other 4K half of the 8K EPROM.

  Instead of a 8K EPROM a 16K, 32K or even a 64K EPROM can be used instead as they come in the same 28 pin package and are pin compatible. Just connect the extra address lines to 0 Volts, 5 Volts or use a switch to control to which voltage they are connected and get extra ROM banks in this way.

  To build it I've used some common Vero board that covers just the space of the two IC sockets on the Ace's PCB board. Any bigger and it can cause problems to fit because of the speakers location or connecting an interface via the edge connector may not be possible anymore.

  The pins that fit into the ROM sockets are made of plain wire that was looped through two Vero board holes before they where soldered. You could also use pin headers or a wire wrap socket which is easier.But because these pins are much thicker they may wear out the Ace's ROM sockets and may cause bad contacts when trying to insert ROM's into the Ace's sockets again. It is also recommended to stick some vinyl tape to the bottom of the Vero board so it will not cause any shorts while fitted into the sockets.

Edwin Blink


Notice the pin under the switch which connects to the 'chip select' on the second Ace's EPROM socket.

Here the pins that connect to the first Ace's EPROM socket can be seen, the 'chip select' pin for the second Ace EPROM socket is not very clear!

  


EB ROMboard in use