Agilent Technologies 45A, 46A Svga Display Card, Gpib Interface Card, Probe Power and Control

Chapter 8: Theory of Operation

Block-Level Theory

SVGA Display Card

The SVGA Display Card controls the flat-panel display monitor. There are two major video paths on this board. The first is used by the system controller on the motherboard to draw all general display elements, including the grid, status indicators, and toolbars and menus for the graphical interface. This is handled through a standard VGA chip, BIOS, and DRAM, similar to a standard PC VGA interface. The other path is the video input from the scope interface board, which is multiplexed with the main video to produce the video signals for the flat-panel display. The video from the scope interface board is the waveform display data. The second path is used to provide the fastest possible display update rate, which would not be possible through the standard bus interface to the display controller.

GPIB Interface Card

The GPIB Interface card provides IEEE-488.2 standard bus services for the oscilloscope. The card interfaces the bus to the motherboard system controller, allowing the system controller to receive and process GPIB commands and return data to the bus. The circuit consists of three main components. The GPIB controller provides an interface between the microprocessor system and the GPIB in accordance with IEEE 488 standards. An 8-bit data buffer and 8-bit control line buffer connect the GPIB controller to the GPIB bus. The GPIB is a 24-conductor shielded cable carrying 8 data lines, 8 control lines, 7 system grounds, and 1 chassis ground.

Probe Power and Control

The Probe Power and Control board provides filtered, regulated power to the front-panel AutoProbe interface. It also provides serial communications capability , offset and probe detection and identification circuitry. All of these are interfaced to the probe through the conductive pads surrounding the BNCs. Using the facilities of this board, the Autoprobe interface can supply power for active probes, notify the oscilloscope operating system when a probe is connected or disconnected, identify the probe type to the oscilloscope operating system for automatic configuration, and communicate with the probe to support advanced probe functionality.

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