Hardware Reference
In-Depth Information
diodes and are used to protect the transistors from reverse bias. The transistor loads are the
windings in the stepper motor. The windings are inductors, storing energy as a magnetic
field. When the current is cut off, the inductor dispenses its stored energy in the form of
an electric current. This current attempts to flow through the transistor, reverse biasing its
collector-emitter pair. The diodes are placed to prevent this current from going through the
transistors.
For higher-torque applications, the normal full-step sequence is used as shown in
Table 7.13. For lower-torque applications, the half-step mode is used and its sequence is
shown in Table 7.14. To control the motor, the microcontroller must output the values
in the table in the sequence shown. Tables 7.13 and 7.14 are circular in that after the last
step, the next output must be the first step. The values may be output in the order shown
to rotate the motor in one direction, or in reverse order to rotate in the reverse direction.
It is essential that the order be preserved even if the motor is stopped for a while. The next
step to restart the motor must be the next sequential step following the last step used. The
mechanical inertia of the motor will require a short delay (usually 5 to 20 ms) between two
steps to prevent the motor from missing steps.
Q4
PP3
Q3
PP2
Q2
PP1
Q1
PP0
Step
Value
1
on
on
off
off
1100
2
off
on
on
off
0110
3
off
off
on
on
0011
4
on
off
off
on
1001
Table 7.13 Full-step sequence for
clockwise rotation
Q4
PP3
Q3
PP2
Q2
PP1
Q1
PP0
Step
Value
1
on
off
off
off
1000
2
on
on
off
off
1100
3
off
on
off
off
0100
4
off
on
on
off
0110
5
off
off
on
off
0010
6
off
off
on
on
0011
7
off
off
off
on
0001
8
on
off
off
on
1001
Table 7.14 Half-step sequence for
clockwise rotation
 
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