Dsa 0026528
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DC Servo Motor Control Application Brief PIC17C756A Market: Motion Control H-Bridge Driver P I C 1 7 C 7 5 6 A DC Motor #1 Encoder PLD 16R8 Direction Up_Count Down_Count PWM1 I/O CAP1 CAP2 H-Bridge Driver DC Motor #2 Encoder PLD 16R8 Direction Up_Count Down_Count PWM2 I/O CAP3 CAP4 φ1 φ2 φ1 φ2 APPLICATION DESCRIPTION The PIC17C756A microcontroller is an excellent choice for cost-effective servo control in e mbedded applications. With two PWMs and four Captures, position and velocity servo control for two motors can be accomplished. (Velocity-only control can be done for three motors.) The D/A for control of each DC motor is accom- plished by one PWM. An H-Bridge is used to trans- late the PWM into usable voltages and currents to drive the motor. Feedback (quadrature data) on the motor goes from the encoder to a programmable logic device (PLD), which is translated into Up_Count and Down_Count pulses. This informa- tion is captured by the PIC17C756A and used in its calculations to control the motor. The PID (Proportional, Integral, Differential) algo- rithm is widely used and, although not the optimum controller for all applications, it is easy to under- stand and use. The PIC17C756A can perform the PID control calculation in less than 100µs (@33 MHz), allowing fast control loop sample times. For more details on how to implement motor con- trol, refer to AN532 Servo Control of a DC Brush Motor .
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