Oki Microline 390, Maintenance Manual, Page: 29 / 174

(4) LSI
The MSM6990 is an external interface and motor control It has the following functions:
A: External interface controller
(a) Parallel interface function
The parallel interface function mode is selected when the level of the mode selection signal
(ISEL) is high. In this mode, to are used as an input port; the parallel data received
through the interface connector is latched in synchronization with the strobe signal
and is sent to the CPU in synchronization with the RD signal. In this mode, the MSM6990
also sends BUSY, ACK, PE and SELECT signals to the parallel interface connector in
synchronization with the WR signal.
Serial interface function
The (ISEL) signal goes low and the serial interface function mode is selected only when the
serial interface board is installed. In this mode,
to IFD8 are used as an input port;
parallel data received from the serial interface board is sent to the CPU in synchronization
with the RD signal. In this mode, the MSM6990 sends SSD, RTS, and DTR signals to the serial
interface connector in synchronization with the WR signal.
p o r t s
The MSM6990 has a output port and a input port. It sends control signals
in accordance with the commands from the microprocessor.
The input port is also used to read information from the operation panel switches, etc.
Address latch
The address latch latches the low-order 8 bits of the address bus to These bits are
used as an address for read/write operations with peripheral devices. Latching of to A7)
is necessary because these 8 bits are also used as the data bus.
8: Motor controller
(a) Spacing speed control function
This function accelerates and decelerates the spacing motor in accordance with commands
from the microprocessor and controls the spacing motor speed in each printing mode.
Dot timing generation function
This function generates the dot-on timing signal synchronized with the printing speed
in accordance with output (PHASE A, 8) of the encoder disk on the spacing motor,
and sends this timing information to the microprocessor.
(5) CGROM
The resident character fonts are stored in the character generator.
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