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Theory of Operation
3.4
Microprocessor
The microprocessor (a Motorola MC68340) is a central processor unit
which supervises system functions, executes the plotter firmware,
manipulates data, and controls input/output data busses. It has two
built-in serial ports, a two channel DMA controller, a timer module, a
clock generator, and an on-board chip select generator. One serial
port connects to the Mini-Din connector which can be used to
communicate with the host computer; the other serial port interfaces to
the Keypad/Display module. One DMA channel supplies data to the
gate array for jet firing; the other DMA channel is used to receive data
through the parallel port or the serial port when using a high speed
serial mode. One timer generates a servo interrupt every millisecond;
the other is used for timing the Stepper Motor.
The phase-locked-loop (PLL) frequency synthesizer generates the
16.777MHz system clock from a 32768Hz crystal reference.
The chip select generator is programmed to generate chip selects at
the appropriate addresses, with the appropriate data size (byte, word)
and with the appropriate number of wait states.
CADJET 2
2-7
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