IMSAI - RAM 4A Card
This was an update of IMSAI's first
4K RAM board. It
was a well designed board and had nice features like write protect
and memory access LED's
The IMSAI RAM 4A board provides up to 4K
bytes or static random access memory. The board was implemented with 2102-style
memory chips that each have the capacity to store 1024 words of one bit for each
word. Thus eight chips are used to store one block of 1024 eight-bit words. Up
to four sets of eight-chip units were used on the board, giving a maximum
capacity of 4096 eight-bit words.
Each eight-chip unit had the circuitry
to allow or prevent the ability to write information into their memory storage
space. This "write-protect" feature could be controlled either by software
commands or from the computer front panel. Software commands could both affect
the write protect and test the status of the write protect. If a program
attempted to write into a write-protect block of memory, an interrupt was
generated. (This feature may be disabled if desired.) Four red LED's are
provided to indicate the protect status of each of the 4K blocks of memory.
Four green LED's are also provided which illuminate when their respective block
of memory is addressed. The RAM 4A board supported a front panel write protect
switch. If the machine was stopped, the 1024 word block at which the machine
address is pointing will have its memory write protect status affected through
the use of a PROTECT/UNPROTECT switch on the front panel. Attempts to write
into this section of the memory will, of course, not succeed. The RAM 4A board
was designed to allow the user to provide battery backup power.
Trickle-charging facilities to allow the battery to be charged while the
computer is running may also be installed on the board by the user.
The manual (updated in 2002) for this board can be
Other IMSAI S-100 Boards
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