Agilent Technologies 34970A, Service Manual, Page: 122 / 273

Floating Logic
Unless otherwise noted, components in this discussion are located on
the A1 circuit assembly (34970-66501).
The schematics are included
in Chapter 8 starting on page 224.
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.
Chapter 5 Theory of Operation
Floating Logic
120