Book Analog Interfacing to Embedded Microprocessors
Figure 7.19
SGS-Thompson L297.
windings using chopping. It has an internal oscillator, comparators, and chop-
ping logic. The oscillator frequency can be set by using an external resis-
tor/capacitor, or an external clock can be used. The chopping clock is also
used to time turn-on and turn-off of the phases to prevent shoot-through.
The L297 provides four phase outputs (ABCD) and two inhibit outputs for
chopping (INH1, INH2). An open-collector HOME signal goes low when the
L297 phase outputs are at the home position (ABCD = 0101). The L297 can
control a stepper in half or full steps.
DC Motors
Figure 7.20 shows a cross-section of a DC motor, sometimes referred to as a
PMDC motor (for permanent magnet DC motor). A DC motor consists of a per-
manent magnet stator and a wound rotor. Connection to the rotor windings
is made with brushes, which make contact with a commutator that is affixed
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