5 Theory of Operation
128 Keysight 34970A/34972A Service Guide
Floating Logic
Unless otherwise noted, components in this discussion are located on the A1
circuit assembly (34970-66501).
The floating common logic controls the operation of the entire instrument. All
measurement control and remote interface command interpretation is performed
in the main controller, U205. The front panel controller, the I/O controller, and all
of the plug-in module controllers, act as slaves to U205. The floating common
logic is comprised of the main controller U205, custom ASIC U209, calibration
memory U201, 12 MHz clock oscillator U204, and microprocessor supervisor
U104.
The microprocessor supervisor U104 performs the following functions:
– Monitors the regulated 5V floating supply and generates the reset signal for
main controller U205 when the voltage drops below operating levels.
– Monitors the unregulated side of the 5V floating supply in order to generate an
early warning signal (PWRFAIL) when power is lost.
– Provides automatic switch over to the battery BT101 for the +5V_NV supply
when the 5V_FLT supply drops below the battery voltage.
– Blocks the main controller’s write signal (WR_N) while the 5V_FLT supply is
below operating level.
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