Theory
of
Operation
2-11
Stack Boards
Board types
and
functions are described
in
the following paragraphs. Each board has a self-test that
runs on powerup or system reset. Self-tests are described
in
Chapter 3.
CPU Board
Two types of CPU board perform
all
the central processing
for
the computer. The
first
type of CPU
contains a clock buffer
and
a CPU chip.
All
CPU microcode, and the hardware to decode
and
execute instructions, are included
in
the CPU chip.
The second type of
CPU board contains an additional three math chips (add/subtract, multiply,
and
divide) to provide floating point,
32
bit or
64
bit,
double precision math solutions. The CPU sends
control information
and
data to the math chip registers. The answer
is
returned to the CPU a
few
computer states later. These math chips are invisible to the operating system.
lOP Board
The lOP board performs
I/O
processing and drives the I/O bus. The lOP board actually consists of
two parts: the board assembly itself and an attached buffer printed circuit board. The buffer pc
board
is
attached to the lOP board by a 50-pin connector. Clamps and screws ensure a solid
physical connection.
The clock buffer
and
the I/O processor chip are on the lOP board. The buffer pc board contains the
five
bi-directional buffer TTL packages that drive the
I/O
bus. The buffer pc board also contains
several resistor packages and a transistor package. The resistor paks terminate the
I/O bus
and
its
characteristic impedance. The transistor pak holds the reset signal on the
I/O
bus during a power-up
and
power-down sequence.
RAM
Board
There are three types of
RAM
boards available for use
in
the stack. They can be installed
in
any
combination, but the 1 Megabyte boards must be used
in
pairs. The 256K byte
RAM
is
a finstrate.
The 512K byte boards
and
1 megabyte
RAM
boards are polystrates. Each board has a memory
controller,
RAM
chips, and clock buffers.
Load Board
The Load Board consists of load resistors to ensure the correct power supply load for certain stack
configurations. The load board
will
be used when:
• The stack consists of
one
CPU,
one
lOP, and
one
512K
RAM
board .
• The stack consists of one CPU,
one
lOP, and six or less 1 Megabyte
RAM
boards.
Stack Motherboard
The stack motherboard interconnects the 12 board slots via the memory processor bus. The two
25-pin connectors at the bottom of the stack provide power and some control signals to the stack
motherboard.
Clock Board
The clock board provides clock signals to the processor. This board electrically interconnects to the
stack motherboard via a 9-pin connector. The clock board attaches to the stack motherboard with
two screws.
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