created 22.08.2008, last changes: 30.03.2009 ps

# >>> Apple II Schematic Diagrams <<<

These drawings are based on reverse-engineering. They should help you fixing your appliance or just teach you how it works. I do not guarantee that they are free from errors, so use them on your own risk. Please note that the artwork was done by me, but the copyright for the circuit itself is held by the manufacturer. Parts of these circuits may be protected by patents preventing you from a commercial use.

- A 16k RAM card. I think this design is from Microsoft. It has three status LEDs and snitches its refresh signals from the mainboard. For that purpose, one RAM chip is removed, placed on the card, and connected to the mainboard via a ribbon cable.

- A 256k RAM card that uses self-refreshing 4165 chips. Manufacturer unknown.

- EPROM Writer I. Manufacturer unknown. The EPROM type (2708..2764) is selected with a DIP jumper that plugs into one of four sockets.

- Extended 80 Column Card for the Apple IIe, by Apple Computer. You had to buy this board to enable the IIe's built-in 80 column text and double-hires modes. Besides that, the board provided another 64kB RAM, mapped parallel to the main memory. Clones were available from different manufacturers.

- Another famous 256k RAM card, the IBS AP17. IBS was a German company that made high-quality peripherals for the Apple II series. Famous are their InteMex boards. InteMex means "intelligent memory expansion", which means RAM (64kB to 1MB) plus CPU (6809, Forth-6811, Z80B, 68000!).

- As an American product, the Apple II generated a NTSC video signal. To see something like colors on a PAL TV, you needed this PAL card. Don't forget to do the 50Hz modifications decribed in the Reference Manual, and to replace the crystal with a 14.025 MHz part. This design is from an unknown Taiwanese supplier, but the original one from Apple Computer is very similar. It is ingenious how the TCA650 PAL decoder is mis-used as an encoder.

- I do not know who designed this Printer Interface, but it is simple and works fine.

- This is one of my own designs, a Serial/Parallel/DataLink interface card. It features an EPSON-compatible printer port, two RS-232 interfaces and a syncronous interface called DataLink I used to control my Märklin model railway. Eight slots are not enought when you are really interested in hardware, so around 1990 I combined these three separate cards into one. One of the 6551 ACIAs uses the same adress space as the SSC, so that software written for that card (including ADT) could be used.

  Serial/Parallel/DataLink interface, build on a prototype board.

- Run CP/M on the 6502-based Apple II with the Microsoft Softcard. DMA allowed a Z80A to share RAM and peripherals with the 6502. This card was cloned by many companies. Some used a PROM for the address translation, instead of the adder.

- Most of the Apple clones had a smart feature: a keyboard with lowercase and a keyword macros. Instead of having to type "LOAD" you just pressed 'FUNC' + 'L'. Unfortunately the guy who invented this misspelled some of the commands.

- The Wildcard is a hardware debugger that allowed to save a snapshot of the RAM memory to disk. Bad guys used this board to crack copy-protected software, good guys to debug their assembler programs. The schematic is derived from a Taiwanese board, manufacturer unknown.

- XEBEX Sider was a hard disk solution for the Apple II, and the interface card is a SASI controller. SASI is SCSI before the standard was issued.

- An Apple IIc does not provide any slots. Nevertheless, there was a Z80 Softcard available, which plugged into the 6502 CPU socket. My board is yellow and bears the name "Cirtech". The part numbers were scraped off from the ICs to prevent piracy, but as the circuit itself is well-known, guessing the types was not too difficult.

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