THEORY OF OPERATION
Internal Modulation Oscillator 2-13.
The modulation oscillator is made up of two sections; a periodic wave generator and a
pulse generator. Both functions are implemented in a custom integrated circuit and are
synthesized from the main reference frequency source of the 6080A/AN.
The periodic wave generator frequency can be set from 0.1 Hz to 200 kHz with
resolution of 0.1 Hz. It is the modulation source for the internal AM, FM, øM, and
pulse functions. The oscillator is based on an algorithmic wave generation method,
which provides a very accurate and stable signal source of high purity and low
harmonic distortion level. The main function of this system is implemented in a custom
integrated circuit. The waveform data is stored in two EPROMs.
In the pulse generation mode, frequency can be set from 10 Hz to 200 kHz, which
results in a pulse period of 0.1 s through 500 us. The pulse width can be set from 100 ns
to 100 ms, with resolution of 100 ns.
Power Supply Description 2-14.
The power supply is a linear design providing + 15V, -15V, +5V, +37V, +30V, +24V,
+23.4V DC, and 6V AC to the signal generator. All the power supplies are series-pass
regulated except the 6V AC display filament supply. A fuse/filter/line-voltage selector
allows the signal generator to operate from 115 or 230V AC.
DIGITAL CONTROLLER SOFTWARE DESCRIPTION 2-15.
The signal generator software is executed on an 68HCOOO microprocessor located in
the A13 Controller PCA. The instrument program is stored in 256K bytes of ROM.
The program stack and RAM variables are stored in 16K bytes of static RAM. A
battery-backed CMOS RAM contains 4K bytes of non-volatile memory for front
panel setups, and 4K bytes of non-volatile calibration/compensation data. An 8K byte
EEPROM contains a redundant copy of the calibration/compensation data. The
software provides the following general functions:
• Services the front panel and the IEEE-488 Interface.
• Configures the hardware to produce the required output, then applies calibration
and compensation data to optimize the performance.
• Implements a set of self-test and diagnostic functions.
User Interface 2-16.
The software is implemented with a simple operating system that allows several tasks
to operate in a round-robin fashion. Input and output to both the front panel and the
IEEE-488 Interface execute at a higher priority and are handled as interrupt routines.
At power-on, the software performs a self-test and initializes both the RAM and the
RF hardware. Four tasks are continuously in operation:
• Diagnostic service task
• Front panel Key task
• Knob task
• IEEE-488 task
2-6
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