Mystery Card

One thought on “Mystery Card

  1. It looks like an “Applied Engineering Z80 Plus v1″ – II Documentation Project/Interface Cards/Z80 Cards/AE Z-80 Plus/Photos/

    The user manual is here –

    A Look At This Photo –
    The D780C 40 pin DIL chip in the centre of the card is a clone of the Zilog Z80 CPU. Lots of manufacturers milled these out under various codenames, this one was made by NEC.
    The D780C CPU date code reveals that particular chip was made in the 48th week of 1983. There is another chip on the card (lower left corner SN74LS374N) with a date-stamp of the 38th week of 1984. So the card was made no earlier than this. The Apple //e was released in January 1983, so this card may only be supported by the new features of that particular model.

    This is a “Z80 Card” used mostly for running CP/M software on an Apple 2.

    Why a Z80 CPU card?
    The Zilog Z80 CPU has been used in computers since 1976(!), most of which, at that time, were installed with the CP/M operating system.
    The CP/M operating system and it’s software is written directly in Z80 ‘machine code’ language and so is completely incompatible (will NOT run) on an Apple 2 computer because they use 6502 CPU’s (first made by MOSTEK in 1975). The CP/M operating system had a huge software base in business and industry in the 1970’s and 1980’s so a massive selling point for a computer system at that time would have been whether or not it could run CP/M software. A Z80 card would allow this.
    These cards would have been popular with companies who had already computerised their business but were looking to ‘upgrade’ to the Apple 2 series and the increasingly large volume of broad ranging software and peripheral devices available for that system. Thus a company could take advantage of the overall cheaper computers offered by Apple but still tap into their historic word-processor, database and spreadsheet documents if they had a “Z80 Card”.

    Technical overview:
    The TBP28L22N chip (lower right) is a 256 Byte ROM. This would hold a small ‘bootstrap’ program which points the hardware on the Z80 card at the Apple’s disk drive(s) where the CP/M OS would be available.
    On this particular Z80 Card there is no RAM (user memory). Therefore it is safe to assume that the Apple 2’s main memory on the motherboard would be used by the Z80 CPU on this card – Quite a feat!
    The User Manual ( seems to describe the Z80 and the 6502 being able to be operated sequentially and able to share & read data from common memory areas – even more of a feat!

    A very desirable card (for a geek)!

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