EC8032K

What is it

EC8032K is a self built CBM 8032 based on cards made by Elektuur/Elektor. From 1980 on Elektor developed several computers, starting with the Junior, a kind of KIM-1 clone. The Junior was a bus based system; features, like a video card or a floppy disk controller, could be connected to the Junior by means of a bus. This bus provided all address, data and control lines.
After some time the EC65 and the EC65K followed. These systems could use the cards developed for the Junior as well.

The fact that the Junior is a clone of the KIM IMHO raised the idea to see if the EC65 could be a clone of the CBM 8032. No, it certainly wasn't. But could it be transformed into one? After some study my answer is 'Yes'.

Why the CBM 8032?

As you can read above, I mentioned the 8032, why not the 3032 or 4032? The video card developed by Elektor is based on the Motorola 6845 and can display 25 lines of 80 characters (80*25). The CBM 3032 has a discrete video circuit and can only display 40*25. The 4032, at least the version I know, has a 6845 based video circuit but also only displays 40*25.

What about the later models like the 500, 610, 7x0 and 8x96? For the moment we can forget about the 500, 610 and 700-series as they are equipped with the 6509 processor.
Regarding the 8096 I only can say this: theoretically it is doable but it will take some more effort.

The memory map of the 8032.

- $0000 - $7FFF : RAM
- $8000 - $8FFF : Video RAM
- $9000 - $9FFF : Reserved for expansion ROM
- $A000 - $AFFF : Reserved for expansion ROM
- $B000 - $E7FF : System ROM
- $E800 - $EFFF : I/O
- $F000 - $FFFF : System ROM

As you can see the system needs 18 KB of ROM and a 2 KB gap for the I/O somewhere in the middle of it. The RAM-EPROM card can provide the ROM for the range $B000 to $EFFF, the EC65K CPU card can provide the last 4 KB.
The RAM-EPROM card has to be changed a bit of course to be able to create the needed I/O gap. Some NAND gates provide this function. The onboard RAM is not needed but can be used to fill the $9000-$BFFF area to be used as an EPROM emulator for ROMs normally placed in this range.
This card is meant for a 6502 system, therefore not capable of handling the address ranges beyond the first 64 KB. A signal generated on the 256 KB SRAM memory card should take care of this by enabling the onboard 74LS154 only then when the first 64 KB segment is selected by the 65SC816.

The needed RAM is provided by the already mentioned 256 KB SRAM memory card.

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