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Theory of Operation
SPG 422 Service Manual (B034000 and above)
3–7
Option 2 Board
The Option 2 board produces the additional serial digital test signals that are
available when Option 2 is installed in the SPG 422. The circuitry is identical to
the Bars generation in the standard instrument.
The Test Signal Generator is a complete generator, requiring only a master clock,
a synchronous frame reset, and some setup information from the microprocessor.
On startup, the processor writes the signal configuration information to the
generator and downloads the necessary audio and video test signals into RAM.
Detailed Circuit Descriptions
This section provides detailed circuit descriptions.
Signal names are all capital letters, for example, SIGNAL.
An active low signal (normally denoted by an overscore) is a signal name
enclosed in parentheses, (SIGNAL).
The aside of a signal name is always in square brackets, for example, [SIGNAL].
The aside of an active-low signal is also the signal name in square brackets, for
example, [(SIGNAL)].
The Front Panel board consists of LEDs and switches. The LEDs light on
commands from the CPU, [L0-L17]. The switches provide control commands to
the CPU that determine the state of the output signals.
The CPU consists of the microprocessor, U3, and its associated memory and
buffers. U11 contains the serial bars data. U10 contains the audio data and CPU
codes. U6 is the external data-bus buffer, while U7 and U8 are the external
address buffers.
The Ground-Closure Parallel Remote.
This consists of a latch that samples the
remote data and places it on the external data bus whenever it is polled by the
microprocessor.
Front-Panel Switch Interface.
The Front Panel Interface converts the X-Y data
format of the front-panel switches into data for the external data bus to control
the microprocessor. If the front panel is disabled, then the commands from the
front panel are not processed.
Logic Conventions
Front Panel Board
Digital Board CPU <1>
Digital Board CPU I/O <2>
Summary of Contents for SPG 422
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