HP 3457A Service Manual page 166

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8-20. The Master Processor controls the HP 3457A's measurement process, communicates with the Front
Panel and HP-IB interface, applies measurenlent corrections and performs math calculations. The Master
Processor circuitry consists of a micro-processor, program ROMs, storage RAMS and associated digital
circuitry.
8-21. The HP-IS Interface circuitry provides communication between the master processor and other in-
struments connected t o the interface bus. The HP 3457A master processor receives HP-IB commands
(Remote, Listen, etc.) and control information (DCV, ACV, etc.) and sends measurement data through the
HP-IB interface circuitry.
HP-IB is Hewlell-Packard's implcmcntalion o f I E E E Slandard 488-1978,
"Standard Digifal Infcrfacc /or Programmahlc In~trirmcnlalion" and A N S I MC
1.1.
8-22. The Front Panel interface circuitry provides communication between the User and the Master
Processor. The processor receives control information through the front panel keyboard and returns
measurement information through the front panel display.
8-23. Floating Common Section
8-24. The Floating Common section consists of Input Switching circuitry, an Input Amplifier, Ohms Current
Source, AC t o DC Convertor, Analog T o Digital Convertor, Voltage Reference, Slave Processor, and
Floating Common Isolation Logic.
8-25. The Input Switching section is responsible for routing the input signal t o the proper measurement cir-
cuitry and connecting the Ohms Current Source when making resistance measurements. The input switching
is also used during Auto-Cal and Self Test procedures t o route stimulus and measurement signals.
8-26. The Input Amplifier scales the input signal to maintain a limited voltage range t o the input of the
Analog t o Digital Convertor circuitry. The amplifier also provides isolatio~i between the device being
measured and the HP 3457A measurement circuitry.
8-27. The Ohms Current Source supplies a known current through resistors being measured t o provide a
proportional voltage which can be measured by the HP 3457A. The current source is also used as a stimulus
during the Self Test routine.
8-28. The AC t o DC Convertor is a computing true rms convertor which converts AC input signals between
20 Hz and 1 MHz t o an equivalent DC voltage for measurement by the H P 3457A.
8-29. The Analog t o Digital Convertor uses a multi-slope conversion process t o convert the analog
measurement data t o digital information.
8-30. The Voltage Reference circuit, as the name implies, provides a stable voltage t o the Analog t o Digital
Convertor and the Ohms Current Source for measurement reference.
8-31. The Slave Processor controls the measurement process. Function and range information received
from the Master Processor is used t o control the input switching and A/D convertor t o make the required
measurement. Measurement results are transferred from the slave processor t o the master processor through
the isolation circuitry.

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