Book Analog Interfacing to Embedded Microprocessors
unique positions would require 10 switches and 10 concentric rings on the
encoder disk. Absolute position encoders are extremely expensive. Their
190 Analog Interfacing to Embedded Microprocessors
Figure 7.30
Absolute position shaft encoder.
primary use is in systems where the position of the motor shaft needs to be
known at power-up.
DC Motor Controller ICs
There are ICs that are designed for the control of DC motors. The
LM628/LM629 from National Semiconductor is one typical device. Figure
7.31 shows how these two devices would work in a system. The LM628 has an
8- or 12-bit output word (selectable) for driving the motor through an analog
interface using a DAC. The LM629 has PWM outputs for driving a motor,
using PWM, through an H-bridge.
Both parts use a similar microprocessor interface. There is an 8-bit
data bus, READ and WRITE signals, a chip select, a reset, and a register
select signal
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