CY545 Stepper System Controller
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Another technique, known as chopping, may also be applied to these driver designs. This
approach applies a voltage much higher than the rated value for a short period of time. The
voltage is then turned off for another time period. This occurs many times per step, with the
frequency of switching known as the chopping frequency. This frequency may be controlled by
time, switching at a given rate, or it may be controlled by sensing the current flow through the
motor, switching at a variable rate. This switching technique controls the power dissipation of
the motor, keeping it at maximum torque for any step rate, by adjusting the average applied
power. The highest performance drivers are usually designed as bipolar chopper circuits.
The user should consult design guides available from the various motor manufacturers and
driver circuit designers for additional information.
Interfacing to the 8255
In the example shown in Figure 19.9 below, the CY545 is operating in the parallel ASCII input
mode. In this mode, bit 7 is always zero and b7 line of the CY545 data bus may be tied to
ground. Since the user will normally transfer bytes of data from memory to the output port, the
most significant bit of the data byte may be used to generate the IO_REQUEST strobe, thus
allowing only one 8 bit output port to suffice. Of course, a separate port line may be used to
generate IO_REQUEST, if desired. If the CY545 is operated in the parallel BINARY mode, all 8
data bus lines are used, and a separate IO_REQUEST line is required. Note that in the example
shown, use is made of the fact that the data and the IO_REQUEST signal may be applied
simultaneously in parallel operation. If query commands are to be used, all 8 bits of the data bus
must be free to operate bidirectionally. In this case, it is generally best to make IO_REQUEST a
separate line from the data ports.
© 2002 Cybernetic Micro Systems
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Chapter 19 - Circuits and Examples
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