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Principles of Operation
Introduction
This chapter contains block diagrams, simplified schematics, and related descriptions of the power supply. The instrument can be thought of as comprising two major sections: the GPIB, microcomputer, and interface circuitry; and the power mesh and control circuits. Block diagrams represent the GPIB board, the front panel board, and the power mesh and control board. The descriptions associated with these block diagrams explain the function of each block without describing how individual components within the circuit accomplish that function. Detailed descriptions are provided only for those individual circuits whose operation may not be obvious to the user.
The circuit names and layouts of the block diagrams are the same as used on the complete schematics; however, some items, such as bias supplies, are left off the block diagrams for clarity. In general, circuits are described as they appear on the diagrams from left to right. Signal names that appear on the drawings are printed in capitals in the descriptions, as are
that condition exists. For example, OT is high and OT is low if an overtemperature condition exists. Signal flow is from left to right and top to bottom, unless arrows indicate otherwise.`
The following paragraphs describe the GPIB and the
GPIB Board
Circuits on the GPIB board, see Figure
Primary Microprocessor
The primary microprocessor controls the GPIB/serial link interface, the front panel data communication, and the DFI/RI interface. It communicates with the secondary microprocessor through two serial link data lines that are optically coupled to provide the proper isolation of the user interface from the power mesh. The GPIB board also has a ROM, which contains the operating firmware, and a RAM, which stores variables such as programmed voltage and current and readback values.
Address Switches
The primary microprocessor determines the GPIB address by reading the address switch settings. Two of the address switches determine the
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