Euro-Apple Modifications

V. Sullivan

Modification 3 (Part 2)

Processor Schematics

This is the second part of the EPROM modification. It gives you access to the Integer Basic and original Apple Monitor that are stored in the lower half of the 2732 EPROMs. The modification also re-arranges the ROM select lines and ROM output enable lines to lower the power consumed by the ROMs. This results in cooler ROM operation and a lighter load on the power supply, which will also stay cooler and have more power left for peripherals.

Step 1) Remove the temporary jumper from ROM F8-18 To ROM F8-12.

Step 2) Remove the six ROMs in row F from their sockets and remove the black plastic part of the socket, being careful of the pins.

Step 3) Isolate pin 18 of each of the six ROMs by cutting the foils.This can be most easily done by five cuts on the top of the board, one each under ROMs D8, En, E8, F0, and F8, and by cutting the foil on the bottom of the board that connects to the plated through hole (PTH), under ROM E8. This is the foil that passes between pins 14 and 15 of the 6502 chip.

Step 4) Isolate pin 20 of each of the six ROMs by cutting the foils. This is done on the bottom of the board for all ROMs except DO, where it is done on the top of the board.

Step 5) Cut all foils to/from the following pins EXCEPT keep the foil between EO1-08 and E01-09 on the bottom of the board.

E01-08 <-----> E01-09 (Top) <-----> E01-10

Step 6) Obtain two small switches suitable for mounting on the front panel of your computer and some light stranded wire such as #28. The switches will be used to select between the various software options as shown in Fig 5. The switches should be wired as shown in Fig 4. You should note that the lower half of ROM D8 is not programmed at this time. If you develop machine language routines that you want to access from either monitor while the basic selection is-Integer or from Integer Basic itself you may store them in this ROM between addresses D800 and DFFF.

Software Selection Table

Fig 4 @8k

Step 7) Connect the following Jumpers using #30 wire.



ROM D8-18---------------------PTH which ROM D8-20 USED to connect to.

ROM EO-18---------------------PTH which ROM EO-20 USED to connect to.

ROM E8-18---------------------PTH which ROM E8-20 USED to connect to.

ROM FO-t8---------------------PTH which ROM FO-20 USED to connect to.

ROM F8-18---------------------PTH which ROM F8-20 USED to connect to.

ROM DO-18-----------------------------------------F12-13

ROM DO-20-----------------------------------------ROM F8-20

ROM F8-20-----------------------------------------ROM FO-20

ROM FO-20-----------------------------------------ROM E8-20

ROM E8-20-----------------------------------------ROM EO-20

ROM EO-20-----------------------------------------ROM D8-20

ROM D8-20-----------------------------------------E01-10

E01-08----------------------------------Peripherial Connector O pin 32


It is now time to check modification 3. With both software selection switches open connect the computer as before and turn on the power. The computer should work exactly as before. If it does not recheck your work. You can now try some other software. With switch 1 closed a reset will put you in the original monitor. Basic may be accessed by typing "Control B. Return". You return to the monitor by typing "Call-151, Return". If switch 2 is closed when you access Basic you will be in Integer Basic with the prompt a>". If you are in either monitor the prompt is "*". At this time you should get some books and start reading. Again I suggest that you use the computer for a few days to gain experience and to make sure that everything will continue to work.