Front Panel Group; A3 Front Panel Interface Board - Keysight N9923A Service Manual

Theory of Operation

Front Panel Group

Front Panel Group
The front panel group consists of the following assemblies:
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—
Refer to
front panel group.

A3 Front Panel Interface Board

The main function of the A3 front panel interface board is to support the user
interface but it also contains the digital power supplies.
Microcontroller and CPLD
The Microcontroller and CPLD sense the keypad keys and the RPG (rotary
pulse generator) knob on the front panel. The Microcontroller communicates
with the A5 system board via a USB interface.
There is no separate ID EPROM on the A3 front panel interface board. All ID
information is stored in the Microcontoller.
Front Panel LED's and ON/OFF Button
The power for the Keypad LED's generated on the A3 front panel interface
board is derived from the +5 V digital supply. The Keypad LED's are turned on
for a few seconds following each key press. This function is controlled by the
firmware on the A6 SOM board.
The On/Off LED is controlled by a signal from the A5 system board. The
connections for the On/Off Button and LED are direct to the A5 system board.
Real Time Clock Battery
The battery for the RTC (real time clock) on the A6 SOM board is located on the
A3 front panel interface board and is connected to the A6 SOM board via the
A5 system board.
Backlight Power
Power for the backlight on the A2 LCD assembly is generated on the A3 front
panel interface board. Digital 5 volts is converted to approximately 25 volts.
The actual voltage determines the brightness of the backlight. Two control
lines from the A5 system board control on/off and intensity functions. These
control lines are driven by the system monitor microcontroller on the A5 system
board.
5-4
A3 Front Panel Interface Board
A2 LCD Assembly
Figure 5-1 for a simplified overall block diagram which includes the
Keysight N9923A Service Guide