HP M2350A Service Manual page 74

Understanding the Computer Module
The Function Cards
Real Time Clock
There is a real time clock chip that is used to output a one second clock to the MPB. The chip
receives its power from a super-capacitor when power is lost. The worst case would power the
chip for 100 hours but more typically the supply would last 255 hours or over 10 days.
Error / Status LEDs
The card has six LEDs. There are three error and three voltage indicator LEDs on the Utility
CPU card. The function of each is described in the following list. They are:
1 MPB Error LED (red) when lit indicates there is a problem with the MPB Interface Chip.
2 Error/Status LEDs (green), connected to the processor via the output latch, are under
software control and may be implemented to indicate a hardware failure on the card during
the boot phase, when no MPB messages can be sent. When the system is running they may
also be used to reflect the status of the card.
3 Voltage indicator LEDs (green) are used to monitor the presence of the DC/DC converter
voltages + 12V, -12V and +5V on the utility bus.
Timing Generation
The Utility-CPU derives the clock signals from a 40 megaHertz oscillator. The output is applied
to a divide-by-2 network to produce the main 20 megaHertz system clock. The Utility-CPU
provides, for internal use, the 16MHz and, 1OMHz CPU clocks and an inverted 10 MHz Local
clock.
Two other clock signals produced are the 8MHz clock for the HP-HIL Chip and 78kHz sent to
the Rack Interface to be used as an excitation. signal for the invasive pressure transducers and
to synchronize the plug-in module power supplies.
SDN Synchronization
Although this is performed by the Utility CPU Card, refer to the SDN Interface functional
description.
n
Provides Central Utility functions:
Real Time Clock - Buffered power supply (~100 hours).
System Clock.
32ms kame Clock.
2ms
Sample Clock.
Power-On Reset.
Voltage indicator LEDs for + 12V, -12V and + 5V.
n
EEPROM (32 kilobytes). System Configuration.
n
HP-HIL Master controller.
n
SDN Synchronization.
n
Rack Interface with excitation signals for plug-in modules..
n
Error LEDs (3).
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