Fluke 8842a instruction manual Keyboard, Digital Controller

Theory of Operation	5
KEYBOARD
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Figure 5-12. Vacuum Fluorescent Display

The Digital Controller sequentially enables the G lines by applying +30V dc (nominal). When a G line is enabled, electrons flow from the filament to the enabled grid. If a P line is enabled (i.e., raised to a nominal +30V dc by the Digital Controller), the electrons continue past the grid and strike the respective plate, causing it to glow.

5-26. KEYBOARD

The keyboard consists of a silicone-rubber switch matrix located over metalized epoxy contacts on the printed wire board. Each button contains a conductive pad that shorts two contacts when pressed.

5-27. DIGITAL CONTROLLER

The Digital Controller (Figure 5-13) consists of the In-Guard μC (U202), External Program Memory (U222), Calibration Memory (U220), Keyboard/Display Interface, and associated components.

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