TM 5-6675-320-14
x .
Memory timing.
The memory timing generates the necessary waveforms from the
microprocessor control signals to insure proper timing for the memory and I/O data
t r a n s f e r s.
A typical READ cycle begins when the microprocessor places an address on
the bus.
One clock period later, STM goes true indicating that the address is valid
and that the address latches should store the information.
One clock period after
receipt of STM, the memory timing sends back UMC.
At this time, the microprocessor
removes the address from the bus.
One-half clock period later, XSMC goes high which
allows the memory output drivers to be enabled.
At the trailing edge of SMC, data
must be stable in order for the microprocessor to store the data in its accumulator
r e g i s t e r .
At the same time, the output drivers are disabled.
y . M a i n P C A A 2 i n t e r n a l I / O c i r c u i t r y.
T h e i n t e r n a l I / O c i r c u i t r y p r o v i d es
buffered interconnection between the front panel PCA A3 and the processor circuits.
A front panel READ will put the status of the front panel switches on the plotter
TTL bus.
A front panel WRITE causes the selected front panel LEDs to light up.
READ registers 23, 26, and 27 are used to put front panel PCA data on the TTL bus,
while WRITE registers 21, 23,,
and 27 are used to enable the LEDs on the front panel
assembly.
These registers are stored in memory locations 20 8 t h r o u g h 278 a n d a re
decoded in the microprocessor circuitry by U33 and U38 using READ, RAL, and addres-
ses A0-A2.
z . F r o n t p a n e l P C A A 3.
The front panel PCA A3 provides a means for the operator
to set CHART HOLD or CHART LOAD, and to manually select a pen, control pen up or
down, and to enter certain position data to the plotter. The operator may also
receive status information concerning the plotter operation from the LEDs on the
f r o n t p a n e l .
The front panel PCA circuits interface with the main PCA A2 through
t h e i n t e r n a l I / O c i r c u i t r y .
The front panel PCA houses switches which indicate to
the plotter which pen stalls are loaded with pens, or if a pen is presently in the
pen arm.
The PCA also provides an interconnection for the X- and Y-limit switches.
aa.
Main PCA A2 memory circuit.
The memory capacity of the plotter is 9k
s i x t e e n - b i t w o r d s .
The memory includes the following:
(1) Read only memory (ROM)
8192 words of ROM. (8k x 16)
(2) Read/Write random access memory (RAM)
1024 words of RAM. (1k x 16)
ab.
Read only memory.
The ROM consists of two 8-bit wide mask programmable ROMs
configured as 8k of 16-bit wide memory.
ROMs U55 and U56 are 8k devices, and they
represent memory locations 000008 through 177778.
These ROMs contain the firmware
instructions to drive the plotter and communicate with the HP-IB controller through
the I/O.
Program execution begins at memory location 408 after the micro-
processor receives the power-on pulse.
ac. Random access memory.
The RAM consists of four 1k by 4 Read/Write Memories
U64, U65, U66, and U67 configured as 1k by 16.
The RAM is used as temporary
storage for various plotter operations and as a buffer for incoming data. The RAM
occupies memory locations 760008 through 777778.
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