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Service Guide ML320/ML321
Chapter 2 Principles of Operation
Large Scale Integrated Circuitry (LSI)
For the Rev A, B, and C printers, the LSI is Q11 - MSM6990
For the Rev D printers, the LSI is Q3 - 7U042-026.
This is an external interface and motor control LSI. It performs the following functions.
External Interface Controller
Parallel Interface Control
This circuit supplies signals used by the Centronics parallel interface.
Serial Interface Control
This circuit supplies signals used by the RS 232-C serial interface.
I/O Ports
Control signals are sent in response to commands input from the microprocessor.
The input port is used to read information on the printer's condition.
Address Latch
It latches the low order eight bits of the address bus (A0 to A7). These bits are used as
addresses for read/write operations with peripheral devices.
Motor Controller
Spacing Motor Control
This function accelerates and decelerates the spacing motor in accordance
with commands from the microprocessor and controls the spacing motor
speed in various printing modes. Motor speed and direction are determined
by monitoring the signals PHASE A and PHASE B, which are provided by
the encoder on the spacing motor.
DOT Timing Generation
This function generates the DOT-ON signal (IPT), which synchronizes the
print wire firing in accordance with the signals PHASE A and PHASE B.
This timing information is also sent to the microprocessor.
