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Table 10.1 Full-Step Sequence
b
d
a
c
On — — — Output pins of UCN-5804
(see Fig. 10.7)
— On — —
— — On —
— — — On
Table 10.2 Half-Step Sequence
a b c d Output pins of UCN-5804
On — — —
On On — —
— On — —
— On On —
— — On —
— — On On
— — — On
On — — On

Pin 14 is the direction. When this pin is tied low or connected to
220
ground, it will follow the sequence in either Table 10.1 or 10.2
starting from the top line and working downward. When this pin is
tied high (15 V), it will reverse the sequence direction starting
from the bottom and working its way to the top.

Using the UCN-5804
Figure 10.8 is a schematic using the UCN-5804. The clocking signal
is provided by the 555 timer. The clocking signal may be increased
or decreased using potentiometer V1. Varying the frequency of the
clock signal directly controls the speed of the stepper motor. In this
chapter we show how the PIC microcontroller can drive a stepper
motor with or without specialty components.
In this schematic, three manual on/off switches control additional
functions. These pins that the switches are connected to can also
be controlled by the input/output (I/O) pins off the basic stamp
microcontroller. The switch connected to pin 15 is the enable pin.
When brought high, this pin disables the output of the UCN-5804
chip, stopping the stepper motor.
The switch connected to pin 14 controls the shaft’s direction, CW
or counterclockwise (CCW). A switch connected to pin 10 controls
the step/half-step function of the UCN-5804. When pin 10 is
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Chapter ten