Theory of Operation 4
Keysight 34420A Service Guide 111
preserve the isolation of the floating circuitry, measurement and control
information is sent serially through opto-isolators to the Earth Referenced Logic.
The Front Panel Controller recognizes front panel Keyboard presses and controls
the Display. A Level Shift is required to interface the Front Panel Controller logic
levels with the Main Controller logic levels.
The Earth Referenced Logic contains an I/0 Controller slaved to the Main
Controller. The I/0 Controller uses a serial data link to the Main Controller through
opto-isolators. The I/0 Controller provides the GPIB and RS-232 Interfaces as well
as the Voltmeter Complete, External Trigger, and Chart Recorder functions.
Separate Power Supplies are provided for the Floating Circuitry and earth
Referenced Circuitry. The Power Transformer provides the bound between floating
and earth reference. The power supply also provides the line frequency reference
used by the Main Controller and resets the Main Controller after power is applied.
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