Circuit Description - Sharp BE-2520 Service Manual

BE=2520
5-9-2. Outline of printer control
@ Whenever the CPU wants to send or receive data to or
from the printer controller, it will chip select the cont-
roller by means of the signal PRS and the address AO.
Once the printer controller has been selected, the data
can now.-be.transferred-on the data bus lines (DO~D7).
@ Whenever data is to be sent to the.printer controller the
CPU will issue WR (write command) as a low.
@ Whenever data is to be:received-by the CPU from the
printer controller: Ameaning, status information), . the
CPU will issue the RD as a low icici a read condi-
tion).
© The INT signal going to'the CPU i is the interrupt request
signal or busy signal issued. by: the printer controller "
during the print cycle.
5-9-3. Motor Drive Circuit.
7
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'. Mm
iu 1) Ion
'St
MOTo----
MTD
Fig. 14
aad @ : Printer motor
® The motor drive circuit turns on the motor by providing
a ground necessary to allow current to flow through the
motor. -
@ in turning off the motor, we want to insure that the
'motor is turned off as: quickly:as possible: This circuit
accomplished that by putting a direct short across the
motor, thus, giving us a braking effect.
CIRCUIT DESCRIPTION
@ Motor on
1) The MTD signal is issued as a tow:
2) The low is inverted twice, giving a low to the base of
'transistor Q11, turning Q11-off.
3) With Q11 off Vp (#24V) goes to one side of the
motor and is also-sent through a resistor to the base
of Q13.
4) A positive to. the base of Q13 will turn Q13 on,
which provides the ground to the other side of the
motor. Current (lon) is now allowed to flow through
the motor. Motor turns on.
NOTE: Q10 and Q12 are off at this time dué to
the positive voltage (at the voltage divider)
being applied to the base toQ12, * ~
@ Motor off and braking ~
1) MTD is issued as a high.
2) High inverted twice aes us a ncins at Dae of O11,
Q1t >on
3) Q11: on,.a low. (GND) 'through diode to the base of
013 > off
4) Q11: on, also. provide a low (GND) to base of Q10,
Q10>o0n
5) Q10: on > Q12: on, which provide a direct short
across the motor. The motor will go off very quickly.
5-9-4. Timing signal generation
Full wave rectifier Shaper circuit
a ae Was [\
coy Yo VY NT" (During the printer motor
rotation, the timing
generator "'G"' generates
ene (alee Ge See he pie
ON ON
OFF OFF OFF . {Omitted}
Ao Big 15
@: Timing pulse generater (in the printer motor)
When 'the motor' is on and rotating, a generater within the
motor will produce the timing pulse, T(T—T'). This TS
pulse is rectified and shaped to the timing signal T . Dot
wire selection will occur in relation to the timing signal
(T).
5-9-5, Print control
The following is the sequence of events for Ronan,
@ Motor on
— Print head moves in a reciprocative (back and forth)
motion. ;
= Timing pulses (T) are constantly generated.
— Reset pulse (R) is developed every time the head
moves from left to right.
—.Print action occurs only while head is moving from
left to. right (single directional print):
@ The printer.controller-will:issue out the dot select signals
(DOT1 ~ DOT7) to the drivers: The drivers will provide
the ground necessary'to energize the solenoids.
NOTE: The dot solenoid will be Srisigizee once in two
timing pulses.
®@® Refering to Fig. 16 when the dot solenoid is energized, .
the actuating plate is pulled toward. the solenoid. The
dot wire is pushed by the actuating plate which hits the
paper through the ink ribbon forming the dot on the
paper. When the solenoid de-energizes, the wire will be
restored to its original position by the return spring.
Ink ribbon
a
aie |
ele eel
CORES
"a Paper
Wires (x7) cummesmnammcin
'
- Platen
(Side view)
Fig. 16-(a)