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IMSAI - PROM 4 Board
This was an early S-100 EPROM card
taking only 1702's. I cannot locate a good color image. If anybody has one
I will place it here.
![IMSAI PROM-4](PROM-4.jpg)
The PROM-4 board provides up to 4K of
addressable Read-Only-Memory, utilizing the Intel 3702-1702 PROM devices. The
board contained 256 bytes of memory for each 8702-1702 chip installed. Address
lines A0 through A7 are run directly to all PROM positions to select one of the
256 internal byte positions, while address lines A8 through A11 were used to
select and enable one particular PROM position through 8205 decoders. Address
lines A12 through A15 were jumper-selected to determine the board's enabling
address. The board was enabled when the 74LS30 NAND gate (C1 in schematic in
manual) inputs are all high, namely when the selected address appears on the
address bus, and the status line SMEMR is high. The Processor Ready line is
controlled by a 74195 shift register via an 8T97. The 74195 provided a
user-selected memory read delay, selectable with jumpers in the delay select
socket. The 74195 shift register is reset on the rising edge of the inverted
Board Enable (BDENA) signal. When addressed and enabled, an 8702-170Z PROM puts
out its data on the DO through D7 lines. The data output lines of all PROMS are
tied to these lines, and these lines are buffered via 8T97 sections to the DI0
through DI7 back plane bus lines. Power for the card logic is provided by a +5
volt regulator and a -5 volt regulator and a -4 volt Zener diode combination to
yield +5 and -9 volts.
The manual for this board can be
obtained here.
Other IMSAI S-100 Boards
4KRAM
8080CPU
EPROM-Programmer
MPU-B
PIC-8 PIO
PROM-4 SIO
VIO
MIO
FDC (FIB/FIM)
This page was last modified
on
01/08/2011