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Theory of Operation
2-27
One or two additional lOP boards can be added. Each is connected by a 50-conductor ribbon cable
to a connector mounted on the computer rear panel. The ribbon cable provides the lOP bus from
the boards to the connector.
A 97098A I/O Expander can be connected to each additional lOP via the rear panel connector.
Each I/O expander provides eight I/O slots with signal buffering and power supplies. The select
code configuration at the I/O backplane is unaffected by additional lOPs. Select codes 0-6 are
assigned to the I/O backplane; select code 7 is assigned to the system control module; select codes
8-15 are assigned to the first additional lOP; select codes 16-23 are assigned to the second
additional lOP.
System Control Module
The system control module (SCM) provides the operating system with the current time at power-
up, controls the service panel, provides high-temperature and power-fail warnings to the operating
system, supplies the loader ROM for the power-up routines, and provides 2K bytes of battery
backed-up memory. Figure 2-16 is a block diagram of the SCM.
SERVICE PANEL
CONNECTOR
+...L.
BATTERY .::.
-~
ADDRESS BUS
BATTERY
CIRCUIT
~
t'
r'--_S_ER_V_IC_E_P_AN_E_L_K_EY_S _ _ __
ADDRESS
COUNTERS
------u----u--~~\J
POWER SUPPLY
LED
DECODER
g
LED BUFFERS
WRITE
f1
R8 OR
R12
-.,.""-~,,,
READ ADDRESS
R8 OR R12
LOADER
ROM
R4
OR R6
READ/IAr"" ......... - - - - '
_ _ _ _ _
M ____ __
r-----...a()"I WRITE
P~~""'-
_ _ _ __
~
SERVICE
R10
L . .I
PROCESSOR
Q
BUS
STATUS
WRITE R1, READ R2
SERVICE
PROCESSOR
DATA BUS
BUFFERS/
DECODERS
REAL·
CMOS
L.........
TIME
NVM
r- ~
CLOCK
R13
R9
BUFFERS
;~~~ I~I
II
~~~~-~EST
SIGNALr"S ...
~..-.
_ _ ...
,,~S
... IGNALS
CONTROL
"""I)
DATA
POWER
LINES
BUS
SUPPLY
S/SCM
CONNECTOR
SIGNALS ..... - - -..... - - - - - - -......
USCM
CONNECTOR
Figure 2-16. System Control Module Block Diagram
The real-time clock provides date, hour, minute, and second information. This information is valid
for at least 10 days after power is switched off. The service panel interface includes the inputs and
interrupts for four pushbutton switches, and a microprocessor to control the service panel LEOs.
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