THEORY OF OPERATION
The diagnostic service task monitors the instrument status signals. The front panel key
task, knob task and IEEE-488 task process user input. A fifth task controls the RF
output when a frequency or amplitude sweep is active. A sixth task is activated only
when needed to process certain STATUS (out-of-range or malfunction) or REJ
ENTRY (rejected entry) conditions that cause the display to flash. A seventh task is
activated when the automatic user compensation procedures have been initiated.
Calibration/Compensation Memory 2-17.
The calibration/compensation memory contains the instrument-specific compensation
data for the coarse loop compensation DAC, coarse loop steering DAC, sum loop
compensation DAC, sum loop steering DAC, sub-synthesizer compensation DAC,
the Output assembly, and the Attenuator assembly. In addition, the AM, FM, level,
and reference oscillator calibration data is stored there. Since the integrity of this data
is crucial to the performance of the signal generator, redundant copies of the data are
kept in two separate non-volatile memory ICs.
Hardware and software protection schemes guard against accidental destruction of the
data. The rear panel switch (labeled CAL|COMP) must be set to the ON position
before updating the calibration/compensation memory.
The calibration/compensation memory self test verifies the CRC checksums of each
data segment. A detailed report of the compensation memory status can be
interrogated from the front panel or the IEEE-488 interface. If errors are detected by
the self test, the signal generator uses only the valid data segments. See Appendix F for
more information on the compensation memory status codes.
Self-Test 2-18.
At power-on, the signal generator automatically tests the digital and analog circuits. If
the signal generator fails any self-test, the test results are automatically displayed as
error codes. Several special functions are available for additional tests (See
"SELF-TEST DESCRIPTION" in Section 6.) In addition, the microprocessor
continuously monitors hardware status signals.
Status Signals 2-19.
The status of the rear panel REF EXT/INT reference switch is continuously
monitored. The state of this switch is used to display the EXTREF annunciator on the
front panel and to program the reference source.
The RF output of the signal generator is considered usable, but not necessarily
calibrated unless the STATUS indicator is flashing. The STATUS indicator flashes
when the output of the instrument is considered unusable because of a severe
overrange condition or a circuit failure.
2-7/2-8
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