2-14
Theory
of
Operation
Minimum
and
maximum configurations are as
follows:
Finstrate
Minimum Maximum*
CPU 1
3
lOP
1 3
RAM
1 10
* Maximum
of
12
finstrates
per
stack.
Stack
Boards
Board types
and
functions are described
in
the following paragraphs. Each board has a self-testthat
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
Finstrate
The lOP finstrate performs I/O processing
and
drives the I/O bus. The lOP finstrate actually consists
of two parts: the finstrate assembly itself
and
an attached printed circuit board. The pc board
is
attached to the finstrate by a 50-pin connector. Clamps
and
screws ensure a solid physical connec-
tion.
The clock buffer
and
the I/O processor chip are on the finstrate. The pc board contains the
five
bi-directional buffer
TIL
packages that drive the I/O bus. The pc board also contains several
resistor packages
and
a transistor package. The resistor paks terminate the I/O bus with its charac-
teristic impedance. The transistor pak holds the reset signal
on
the I/O bus during a power up/power
down sequence,
and
drives the self-test LED
on
the stack motherboard.
RAM
Boards
There are three types of
RAM
boards available for use
in
the stack. They can
be
combined in any
combination, but the 1 Megabyte boards must
be
used
in
pairs. The 256K byte
RAM
is
a finstrate.
The 512K byte
and
1 Megabyte 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.
09020-90037, rev:
1/85
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