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THEORY OF OPERATION
The IMSAI MPU-A board is structured around the 808ÖA
microprocessor chip, and much of the MPU-A board is wired
to support the 8080A device.
interfacing between the 8080A chip and the data and address
busses, clock and synchronization signals, and the voltage
regulation necessary for the 8080A and other chips.
internal functioning of' the 8080A is thoroughly described in
the Intel 8080 Microcomputer System User's M an u a l .
should be made to this manual for information concerning
the operation and use of the 8080A.
The address lines from the 8080A drive the address bus on
the back plane through 8T97 tri-state buffer drivers.
drivers may be disabled through the ADDRESS DISABLE line on
pin 22 of the back plane.
drivers connect the 8 080's bi-directional DATA IN and DATA
OUT busses.
The direction of data transmission is determined
by the DIRECTION ENABLE line.
in turn controlled by the front panel and the processor
status signals DATA BUS IN and HALT ACKNOWLEDGE.
can be disabled by the DATA OUT DISABLE line on pin 23 of
the back plane.
The 8080A's bi-directional data bus is also connected to the
data bus socket and the 8212 status byte latch.
socket is used to connect the front panel to the bi-directional
bus, while the 8212 latch transfers the status byte to the
back plane via 8T97 drivers.
the STATUS DISABLE line on pin 18 of the back plane.
8212 is latched up by the STATUS STROBE signal of the 8224
clock chip to store the status information for each in
struction cycle.
One K pullup resistors to +5 volts are connected to all
the bi-directional bus lines to ensure that during the
time the bus is not driven, the 8080A reads all I's.
The 8224 clock chip and crystal oscillator
two-phase non-overlapping 2 megacycle system clock for
the 8080A.
These clocks are also driven onto the back
plane through 8T97 tri-state buffered drivers.
5
2
The MPU-A board provides
The 8216 bi-directional bus
The DIRECTION ENABLE line is
These drivers are disabled by
MPU-A
Theory of Operation
Revision 1
The
Reference
These
The 8216
The data bus
The
provide the
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