The lid was already begging to be removed and curiosity demanded it.
The unit contains a MEK6800AB backplane with:
- MEK6800D2 Processor Card
- MEK68 I/O Card
- MEK68MM32 32kB Memory Card
- MEK68R2 Video card
There are several connections to the cards including coaxes for the cassette interface and the video output, and a DIP connector for the RS232 line.
The front panel card (must get a photo) connects to the processor card by a bright red ribbon cable. This was disconnected and that be be deliberate.
The bus interface on the processor uses an edge connector whereas the other cards use a SIL connector. The former is consistent with Motorla EXORciser Bus and the latter is referred to as the Motorola Kit Expansion Products (MOKEP) interface.
The processor card includes the 6800 processor, which seems to be suffering some corrosion – a common occurence with ICs using silver plate rather than tin.
It also has two different Parallel Interface adapters: an MC6821 and an older MC6820 (in a ceramic package). There are two ROMs. One is clearly the JBUG ROM. The other is presumably the CRTBUG ROM. The third ROM socket is unoccupied. There is a 128B RAM which is used by the JBUG ROM program. The 4x 128B RAM sockets in the lower left have been filled with an Australian produced RAM daughter-board that provides a massive 2kB!
There are clearly some mods, one of which i expect is to select between the two onboard monitor programs using a front panel switch. A front panel reset switch is wired directly to the S1 footprint.
The two upper edge connectors are for the PIAs. One of these is used to connect the keypad/display board. The other is user defined – it appears to be used for a small I/O board (get photo) – two relays and drivers, i think.
The keypad/display card connects to the processor card using a ribbon cable. It also has some circuitry for the cassette interface.
The I/O Card is not fully populated. There are two Asynchronous Serial Interface Adapters (ACIA); one for the cassette interface and one for an RS232 port. There is one Parallel Interface Adpater (PIA) and provision for one more. I/O connections are made via loathesome 16 and 24 pin DIL cable connectors. There is a switch to select 300 or 1200 baud on the cassette interface and two RCA connectors for same. There is a manual available for this card.
The video card uses the popular MC6845 video controller. It has 2kB of RAM so should support 80 columns by 24 lines. I have not located a manual for this card. Hopefully it will just work with the CRTBUG monitor and the keyboard otherwise i’ll have some reverse engineering to do.
The RAM card is populated with 32kB of dynamic memory. Again, i haven’t been able to find a manual for this but i assume that it is located at 0000 and overlaps with the processor card RAM and option ROM. Perhaps some of the mods on the processor card take care of this.
The ASCII keyboard uses a mask programmed Intel 8048 microcontroller with what is likely to be a custom version of the General Instrument AY-5-2600 Keyboard Encoder.
