Real-Time Clock/Non-Volatile Memory (Rtc/Nvm) - HP 9020 Service Manual

3-16
Testing and Troubleshooting
Real-Time Clock/Non-Volatile Memory (RTC/NVM)
The keyboard processor board contains the RTC and NVM chips and the battery assembly to
maintain the 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 -
Byte 1 -
Byte 2 -
Byte 3 -
Byte 4 -
Byte 5 -
Byte 6 -
Byte 7 -
Byte 8 -
Byte 9 -
Bytes 10-13 -
Byte 14 -
Byte 15 -
Byte 16 -
Bytes 17-24 -
Bytes 25-44 -
Byte 45 -
Bytes 46-47 -
Bytes 48-53 -
Bytes 54-57 -
Bytes 58-60 -
Byte 61 -
Bytes 62-63 -
Second
Clock Check Byte
Minute
Stack Size (two times number of boards)
Hour
Century
Day of Week
Day of Month
Month
Year
Control Registers
Timer Resolution
Timeout Scan Resolution
Keyboard Initialization Data
Default System Startup Subsystem
Default Mass Storage Unit Specifier
Size of System
110
Buffer
NVM Checksum
Healer CAM Overflow Counter
Last Double Bit Memory Failure Data
Number of 10-Minute Periods Computer is On
Number of Overheat Cycles
Number of Power-On Cycles
The keyboard processor board 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 maintains RTC and NVM data for a minimum of
10 days while power is off.