Address Decoding; Bus Error Logic; Error Leds; Temperature Sensor - HP M2350A Service Manual

Understanding the Computer Module
The Function Curds
Address Decoding
The address decoding logic is used to generate strobes and select signals for the on-board
devices (MPB, SRAM, EPROM). Access acknowledge signals are also generated for all the
devices except the MPB Interface Chip, which generates its own acknowledge signal.
Bus Error Logic
The bus error logic consists of a timer that monitors the microprocessor's address strobe. When
the processor outputs an address on its bus, it asserts the address strobe to indicate that a
valid memory address is available. However, if the signal is asserted for too long then the
logic assumes that the access was not terminated correctly, that is, the address strobe was not
negated or removed. The logic then asserts a Bus-Error to tell the processor that it could not
access the memory correctly.
PFAIL and SYS-RESET
The PFAIL signal is used to inform all other function cards that a SYS-RESET should be
expected from the UTIL-CPU. This is to allow the system to reset all cards synchronously. One
bit of the CPU output latch is used to place PFAIL on the utility bus
The PFXIL signal is asserted for two reasons by the CPU:
1. The CPU detects that a serious error has occurred in the system.
2. The watchdog circuit in the MPB-chip detects a failure in the CPU.
The PFAIL is also asserted by the DC/DC Converter when the power is about to fail.
Error LEDs
There are three error LEDs on the CPC:
One MPB Error LED (red) is used to indicate a problem with a device on the card.
Two Error/Status LEDs (green) 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.
Temperature Sensor
The operating system CPC (slot 22) includes a socketed, replaceable temperature sensor which
will generate an error message if the ambient temperature exceeds 60 degrees Centigrade (140
degrees Fahrenheit), f5 degrees.
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