Microprocessor System - Racal Instruments 2461 User Manual

Microprocessor
System
Theory Of Operation 3-8
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Referring to the block diagram, the processor system is based
on a microcontroller design which drives both the input
conditioning relays, calibration DAC and trigger level DACs.
In addition the processor drives the measurement system and
performs the necessary calculations to produce a result which
is then passed to the VXI interface card processor for
transmission over to the VXI bus if necessary.
The microcontroller used has both a number of static I/O ports
in addition to an externally available address and data base.
This mixture of I/O allows memory mapped I/O for fast
peripherals such as the measurement system while the static
I/O ports are used control of relays, standards, etc.
Firmware is stored in conventional EPROM while non-volatile
constants are stored in a serial EEPROM. Address decode and
further I/O is performed in the EPLD along with the
measurement system
After power up the microcontroller reads calibration data from
the serial EEPROM and the 8X8 bit DAC are initialized. The
measurement system, trigger level DACs and input conditioner
relays, are set to their default values. The system will now wait
for an initiate command, sent via the VXI interface processor,
before a measurement sequence will commence. Alternately,
the operator may command alternative measurement functions
or input conditions via the VXI interface processor.
Any type of command from the VXI bus will be passed from the
VXI processor to the microcontroller via the interface logic. The
content of the message passed will cause the microcontroller
to change various conditions, measurement functions, or
trigger one or more measurement cycles.
Each successful measurement cycle will result in a
measurement result which is transferred to the VXI
microcontroller as soon as it is calculated and before the next
measurement cycle commences.
2461Type C User Manual
Racal Instruments  1998