Brother PT-2500PC, Service Manual

Page: 56 / 79

III - 6
3.2.4 Tape Feed Motor Drive Circuit
Fig. 3.2-3 shows a drive circuit of the tape feed motor which feeds tape and ink ribbon.
The motor is a 30-mm in diameter, 24-pole, and 108-internal resistance stepping motor.
This circuit drives the motor with a bipolar 2-2 phase excitation.
The CPU (#3) controls the motor rotation direction with signals on P104 and P105 and
turns the motor on and off with an activation signal of the driver IC (TA7774F, #2). When
P106 is High, the motor rotates in the direction defined by the signals on P104 and
P105.
(1) Printing in a constant speed
For regular printing in a constant speed, the CPU drives the motor at the rate of 144
pps. To provide buffered starting and stopping for the motor, the gradual
acceleration and deceleration are programmed to consume 8 and 3 pulses,
respectively.
(2) Printing interrupt (margin cutting drive and buffer full drive)
After completion of the current printing, the CPU brakes the motor with 3-pulse
gradual deceleration and then counter-drives it by 20 pulses to stop the motor.
Fig. 3.2-3 Tape Feed Motor Drive Circuit