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Vector Graphic 48K Dynamic RAM
Vector Graph developed two dynamic RAM cards over time. The 48K static RAM was their first.


The Vector Graphic 48K Dynamic Memory Board provided 49,152 8-bit bytes of random access memory, using 24 16K dynamic memory chips. They claimed it could be used in ANY  S-100 bus computer using a Z-80 CPU board -with minor modifications. It occupies the lower 48K of memory, i.e. beginning at 0000H. The Vector Graphic 48K Dynamic Memory Board was a bit of a  breakthrough in cost effectiveness. This was accomplished by combining compact inexpensive dynamic memory chips with the use of the refresh provisions of the -80 CPU. The static RAM boards of the time cost considerably more, take up more space, and require more power. Other dynamic memory boards use complex support logic on the board,   rather than the built in features of the Z-80.  In addition to the above features, the Vector Graphic Dynamic Memory Board quite reliable. Considerable attention was given during design of the board to the elimination of noise. It features a gridded ground plane designed to reduce noise. Accepted design practice was observed in structuring grounds, power supply, and bypass. capacitors.
There were complications however with some systems involving the RESET S-100 line (pin 75). The modification involves changing the reset circuit of the CPU board so that it responds to the short reset pulse generated by this 48K RAM board on pin 55 rather than responding directly to the PRESET signal on pin 75 typically generated by a front panel reset switch. -This modification prevents the CPU from being held in a reset state for longer than 2 milliseconds which would result in loss of memory data, since the memory is not being refreshed while the CPU is in a reset state. The manual below outlines what needed to be done.  There were also problems with old front panel READY line putting the Z80 in an extended wait state thus blocking RAM refresh on this board. Indeed some PROM programming boards/software caused problems for the same reason.  Don't even think about using this arrangement with a master/slave  IEEE S-100 bus system. All in all the arrangement of utilizing the Z80 refresh signal on the bus did not catch on. Better arrangements was to have a refresh controller on the board itself.  The SD Systems ExpandoRAM being a perfect example.
The schematic for this card card can be seen here.
The manual for this card can be obtained here.


Other Vector Graphic  S-100 Boards
Dual FD-HD Controller    FlashWriter-II    Bitstreamer-II   48K-RAM    64K-RAM   8080-Board  
8K-RAM   EPROM  FDC   Micropolis-FDC    Z80-Board    SBC


This page was last modified on 10/25/2013