DSP56857 datasheet(372/662 Pages) FREESCALE

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Counting Modes Definitions

5685X Digital Signal Controller User Manual, Rev. 4

13-6

Freescale Semiconductor

13.7.2 Count Mode

If the Count mode field is set to 001, the counter will count the rising edges of the selected clock

source. This mode is useful for generating periodic interrupts for timing purposes, or counting

external events such as widgets on a conveyor belt passing a sensor. If the selected input is

inverted by setting the Input Polarity Select (IPS) bit, the negative edge of the selected external

input signal is counted.

13.7.3 Edge Count Mode

If the Count mode field is set to 010, the counter will count both edges of the selected external

clock source. This mode is useful for counting the changes in the external environment such as a

simple encoder wheel.

13.7.4 Gated Count Mode

If the Count mode field is set to 011, the counter will count while the selected secondary input

signal is high. This mode is used to time the duration of external events. If the selected input is

inverted by setting the Input Polarity Select (IPS) bit, the counter will count while the selected

secondary input is low.

13.7.5 Quadrature Count Mode

When the Count mode field is set to 100, the counter will decode the primary and secondary

external inputs as quadrature encoded signals. Quadrature signals are usually generated by rotary

or linear sensors used to monitor movement of motor shafts or mechanical equipment. The

quadrature signals are square waves, 90 degrees out-of-phase. The decoding of quadrature signal

provides both count and direction information. A timing diagram illustrating the basic operation

of a quadrature incremental position encoder is provided in Figure 13-2.

Figure 13-2. Quadrature Incremental Position Encoder

-1

PHASEA

COUNT

PHASEB

UP/DN

DSP56857 Datasheet(PDF) 372 Page - Freescale Semiconductor, Inc