Carriage Motor Drive Block - Panasonic KX-P1180 Service Manual

KX-P1180
8.2.5 Carriage Motor Drive Block
The Carriage motor is driven by the four signals from CRA, CRB, CRC and CRD, which are shifted 90 degrees
from each other.
ICQ pins 64 and 65 are used to excite one winding (two phases) of the stepping motor, while pins 6 and
6? excite the other two phases, creating a 2-2 driving system.
The time interval is determined by the CPU's Interval counter clock as generated from the CPU's clock.
This circuit is a chopper drive circuit for fixing the amount of the current through the motor during stepping
and has two threshold voltages (VSH, VSL). 1C11 compares the voltage drop across R85(R86) which is
proportional to the current through the motor. For example, when the voltage drop across R85(R86) is
larger than VSH, IC11 is turned off and Q15(Q14) is turned off, then Q17(or Q16) is :urned off. At the same
time, the current through the motor decreases, because the voltage drop across R85(R86) decreases. When
this voltage drop is smaller than VSL, 1C11 is turned on, and the current through the motor increases.
The amount of current through the motor is fixed during stepping by repeating this process.
These threshold voltages (VSH, VSL) are changed by PB4 (PB2) H or L signal according to the print mode.
When the motor is in the standby state, Q17 and Q16 are turned off, and a holding voltage is supplied to
the motor through R87 and R88.
Timing Chart