Theory of Operation (2635A)
Introduction
2A
2A-3
2A-1. Introduction
The theory of operation begins with a general overview of the instrument and progresses
to a detailed description of the circuits of each pca.
The instrument is first described in general terms with a Functional Block Description.
Then, each block is detailed further (often to the component level) with Detailed Circuit
Descriptions. Refer to Section 8 of this manual for full schematic diagrams. The
Interconnect Diagram in this section (Figure 2A-1) illustrates physical connections
among pca’s.
Signal names followed by a ’*’ are active (asserted) low. All other signals are active high.
2A-2. Functional Block Description
Refer to Figure 2A-2, Overall Functional Block Diagram, during the following
functional block descriptions.
2A-3. Main PCA Circuitry
The following paragraphs describe the major circuit blocks on the Main PCA.
2A-4. Power Supply
The Power Supply functional block provides voltages required by the vacuum-
fluorescent display (-30V dc, -5.0V dc, and filament voltage of 5.4V ac), the inguard
circuitry (-5.4V dc VSS, +5.3V dc VDD, and +5.6V dc VDDR), and outguard digital
circuitry of +5.0V dc (VCC).
Within the Power Supply, the Raw DC Supply converts ac line voltage to dc levels. The
5V Switching Supply converts this raw dc to 5.0V ±0.25V dc, which is used by the
Inverter in generating the above-mentioned outputs. The Power Fail Detector monitors
the Raw DC Supply and provides a power supply status signal to the Microprocessor in
the Digital Kernel.
2A-5. Digital Kernel
The Digital Kernel functional block is responsible for the coordination of all activities
within the instrument. This block requires voltages from the Power Supply and signals
from the Power-on Reset circuit.
Specifically, the Digital Kernel Microprocessor performs the following functions:
•
Executes the instructions stored in FLASH EPROM.
•
Stores temporary data and nonvolatile instrument configuration datain NVRAM.
•
Stores instrument calibration data in FLASH EPROM.
•
Communicates with the microcontroller on the A/D Converter PCA viathe Serial
Communication (Guard Crossing) block.
•
Communicates with the Display Controller to display readings and userinterface
information.
•
Communicates with the Field Programmable Gate Array, which scans theuser
interface keyboard found on the Display Assembly and interfaceswith the Digital I/O
hardware.
•
Communicates with a host computer via the RS-232 interface.
•
Stores instrument setup and measurement data on a Static RAM memorycard
installed in the Memory Card Interface Assembly.
•
Reads the digital inputs and changes digital and alarm outputs.
Summary of Contents for 2620A
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Page 254: ...HYDRA Service Manual 6 20 2620A 1601 s63f eps Figure 6 3 2620A 2625A A1 Main PCA...
Page 258: ...HYDRA Service Manual 6 24 2635A 1601 s64f eps Figure 6 4 2635A A1 Main PCA...
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Page 285: ...Schematic Diagrams 8 8 3 Figure 8 1 A1 Main PCA 2620A 2625A 2620A 1601 s88f eps...
Page 288: ...Schematic Diagrams 8 8 6 Figure 8 1 A1 Main PCA 2620A 2625A cont 2620A 1001 3 of 4 s73f eps...
Page 292: ...Schematic Diagrams 8 8 10 2635A 1001 2 of 5 Figure 8 2 A1 Main PCA 2635A cont s76f eps...
Page 293: ...Schematic Diagrams 8 8 11 2635A 1001 3 of 5 Figure 8 2 A1 Main PCA 2635A cont s77f eps...
Page 296: ...Schematic Diagrams 8 8 14 2620A 4002 CKT 1 CKT 2 Figure 8 3 A2 Display PCA s90f eps...
Page 300: ...Schematic Diagrams 8 8 18 2620A 1003 2 of 3 Figure 8 4 A3 A D Converter PCA cont s82c eps...
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Page 302: ...Schematic Diagrams 8 8 20 2620A 1604 Figure 8 5 A4 Analog Input PCA s92f eps...
Page 304: ...Schematic Diagrams 8 8 22 2620A 1605 Figure 8 6 A5 IEEE 488 Interface PCA 2620A Only s93f eps...
Page 306: ...Schematic Diagrams 8 8 24 2625A 1606 Figure 8 7 A6 Memory PCA 2625A s94f eps...
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