Agilent Technologies E4416A Service Manual page 99

4 Theory of Operation
The TTL inputs are connected to the processor card via in line resistors
located on the interface card and can be used to initiate zero and calibration
cycles on the power meter.
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.
It is advisable to replace the RAM battery A2BT1 every three years. If the battery fails
N O TE
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.
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E4416A/E4417A Power Meters Service Guide