improved "Rex Combi Card"
Date: 2004-08-05 21:01:56

Hi dudes,

Some of you surely remember the "Rex Combi Card". This addon-board, which 
fitted into the the kernal socket on the C-64, not only provided the options to 
switch between 4 C-64-Kernals, but also between 4 inbuilt cartdrige modules 
($8000-$9fff). I managed to make an improved clone of this board by using some 
Eprom (27256 or larger), a few Pull-Up-Resistors and switches and just a single 
AND-Gate (TTL 74ls00 or LS08). 

The schematic described so far:

* Insert a Switch between GND and Pin9 of the cartridge port. This is 
the "module on/off" switch.

* Feed Pin11 of the Cartridge port to the highest adress line of an Eprom which 
is inserted into the Kernal socket (U4 on the 64's board). This highest address 
line must be kept to "1" using a Pull-Up-Resistor, otherwise.

* Properly Chip-Select the Eprom: Make an "AND" between the Chipselect-line 
coming from the kernal socket and Pin11 of the Cart port. The result of the AND 
is being fed to the Chipselect-line of the eprom.

* All other _extra_ address lines of the Eprom: Keep them to "1" using a pullup-
resistor 10kOhm, and insert a switch to optionally toggle the line to GND.

* A0-A12 and D0-D7 and +5V and GND are connected to the Kernal socket as usual.

I'll add a simple schematic for a 2xkernal/2xmodules switch.

I sucessfully expanded it to 8xkernel/8xmodules since the 27c101 Eprom was sold 
very cheap (2 Euro) in a local store.

Have fun with this simple and efficient clone.

ATT / L 

Ein Service von

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