Testing
and
Troubleshooting 3-19
Real-Time Clock (RTC) and Non-Volatile Memory (NVM)
The system control module contains the RTC
and
NVM
chips
and
the battery assembly to maintain
data
in
both chips during power-off states.
The RTC
and
NVM
chips store a clock, system configuration data,
and
service information of
significance to users
and
service personnel. The clock
is
initially loaded from the lOP
and
is
updated
by a crystal oscillator. The RTC chip stores clock
and
calendar data
in
16
four-bit locations; the
NVM
chip has
2048
eight-bit locations
and
stores service
and
configuration data. RTC/NVM
locations
and
contents are as follows:
Byte
0 -
Second
Byte 1 - Clock Check Byte
Byte 2 - Minute
Byte 3 - Stack Size (two times
number
of finstrates)
Byte 4
-Hour
Byte 5 - Century
Byte 6 - Day of Week
Byte 7 - Day of Month
Byte 8 - Month
Byte 9 -
Year
Bytes 10-13 - Control Registers
Byte
14
- Timer Resolution
Byte
15
- Timeout Scan Resolution
Byte
16
- Keyboard Initialization Data
Bytes 17-24 - Default System Startup Subsystem
Bytes
25-44
- Default Mass Storage Unit Specifier (MSUS)
Byte
45
- Size of System
110
Buffer
Bytes 46-47 -
NVM
Checksum
Bytes 48-53 - Healer
CAM
Overflow Counter
Bytes 54-57 - Last Double
Bit
Memory Failure Data
Bytes
58-60
- Number of 10-Minute Periods Computer
is
On
Byte 61 - Number of Overheat Cycles
Bytes 62-63 - Number of
Power-On Cycles
The
system control module contains a nickel-cadmium battery assembly consisting of four batteries
to maintain the RTC
and
NVM
chips during a power-off condition. Because only three batteries are
required,
one
is
redundant. This enables the chips to operate without error
if
one
of the batteries
has a short circuit. The battery assembly maintain RTC
and
NVM
data for a minimum of
10
days
while power
is
off.
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