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Theory of Operation
A2 Processor Assembly
The microcontroller circuits that control all the above functions, and
provide platform for the system software to run on, comprise the
microcontroller itself, memory, and clock and logic circuits. The logic
circuits have the function of ensuring the correct sequencing and decoding
of the control signals for the various peripherals. The crystal oscillator
clock circuit is buffered and distributed to the A4 interface assembly and
the A5 daughter assembly. The program memory for the microcontroller is
FLASH EEPROM to allow for in-circuit programming. The static RAM is
split into volatile and non-volatile blocks, with the power for the
non-volatile RAM being connected to the permanent (battery backed)
power supply.
Note
4-6
It is advisable to replace the RAM battery A2BT1 every three
years. If the battery fails or drops below 3 V the RAM will lose the
following information when power is disconnected from the meter:
Unit Serial Number
Revision letter of Processor Card
Unit Option
User defined setups
User defined sensor calibration tables
Agilent E4418B/E4419B Service Guide
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