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4.3
Operation of the 'Control Section
4.3.1
General
As for the parts location number such as Q mentioned in this
chapter, See Fig. 6-2-
(1)
schematic diagram (LEPS circuit
board) or Fig. 6-2-(2) schematic diagram (LEPU circuit board).
A block diagram of the printer is shown in Fig. 4-7.
The control section consists of a single printed circuit board,
and controls the mechanical section.
It employs a microcomputer
for controlling the mechanical section, and has a 256 RAM with
an I/O port serving as input data buffer, and a character
generator which memorized character patterns.
Input data from the interface is first written into the RAM,
where it is stored.
When data for one line has been inputted,
the printer starts printing.
First, the space pulse motor runs
to move the carriage.
Pulses are applied to the print head to
print characters.
When one line has been printed, the space pulse motor runs
backward to return the carriage to the home position.
At the same time, the line feed pulse motor is driven to move
the paper up one line.
This completes one cycle, and the printer waits for the next
data input.
4.3.2
Outline of Control Circuit
The printer operates under control of the microcomputer, Q2.
As shown in the circuit diagram in Chapter 6, Q2 is the 8-bit
I-chip microcomputer, which has a 1 k-byte ROM, 64-byte RAM
and 8-bit timer.
A control program is stored in the inside ROM,
and runs when the printer is powered on.
Q2's 64-byte RAM is
used as register, and the timer is used for internal control.
A 3.58 MHz oscillator (OSC) is connected to XTLI and XTL2, gen-
erating the basic clock.
The
~CPU
cycle time
~s
about 4.2
~s.
The control circuit has an 8-bit bus line, 16 I/O ports, and
3 terminals as I/O means.
The bus line is connected to Ql for
sending and receiving data and instructions.
The I/O ports are connected to Q3 to address the character
generator.
TO, Tl and INT are used as control inputs.
Ql is the 256-byte I/O RAM with 22 I/O ports.
(The internal
timer is not used).
The I/O ports are used for interface
signals, and as control lines to the step motors.
Q3 is the 2 k-byte character generator PROM.
Addresses are
assigned via the
~CPU
by AO thru AIO, and signals corresponding
to characters are output from 00 to 07, which drive the darlington
transistor array Qll, Q10 (or Tr7 to Tr13) through inverters Q4
and Q6.
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