Electro-Metrics EM-2115, Instruction Manual

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EM-2115 APPENDIX C FUNCTION AND DESCRIPTION
(EM2115C-12)
The LO output from the RF Tuner (A2) is applied to a scaling circuit that, depending on
the RF Frequency Band being used, divides the output by either 100 or 1. This output is applied
to the Microprocessor Board (A1A3).
A regulator circuit within the module provides the +7 VDC supply voltage required by
the prescaler circuitry.
C-14 A1A2 Front Panel Board
(Refer to Figure H.22)
The Front Panel Board is the interface between the front panel displays-switches-
indicator lights and the Microprocessor Board A1A3.
The LED displays for Amplitude and Frequency indication are driven by decoders-drivers
that receive their input data from the Microprocessor Board. The analog meter receives its input
from the Detector Board and is used for relative indication only. It is used for "peaking-in" sig-
nals especially at the narrower bandwidths and then reading the amplitude and frequency from
the appropriate LED display.
The majority of front panel pushbutton switches are part of a keyboard encoder circuit
that provides the logic data keyed in by the switches to the Microprocessor Board. In addition,
the data is supplied to a series of latching circuits that in turn activate LED indicators. The indi-
cators provide a visual indication of the switch function activated.
The sweep function and tuning controls (Main Tuning Control, Fine Tune, Sweep Rate,
Sweep Width, Output Level, Slideback Threshold, Audio Volume, Power) are connected directly
to the internal circuitry or pc board that control these functions.
C-15 A1A3 Microprocessor Assembly
(Refer to Figure H.24)
The internal Microprocessor Assembly contains the control circuitry for the EM-2115.
Information is received from the front panel switches-controls or via the rear panel GPIB Con-
nector, then processed. The resultant logic commands are sent to the appropirate internal circuits
that respond in accordance with the commands received.
The microprocessor chip (U16) is the key element of the control system. It receives, pro-
cesses, and outputs information to the circuitry within the unit. Associated with the microproces-
sor chip are the EPROM (Erasable Programable Read Only Memory) chips (U6, U7), RAMs
(Random Access Memory-read/write memory) (U8-U11), and clock circuit.
The EPROMs are programmed with the permanent information and data required to op-
erate the unit within the specification limits.
The RAM chips are updated during the operation of the unit with information from the
front panel switches-controls, data from logic outputs initiated within the circuitry of the unit, or
via the rear panel GPIB Connector.