Red Lion LEGEND - Manual (Page 18)

PROGRAM COUNTER MODULE
In the Counter Module, the count mode, reset action, and automatic reset
capability are selected. The following flowchart shows only the Counter portion:
COUNT MODES
There are seven available count modes, which can be used with the
separate external Inhibit terminal. Input A signal is used for count and the rate
input. Input B is used in combination with Input A for Count Control
Direction, Quadrature counting, Anti-coincidence Add/Subtract or
Anti-coincidence Add/Add counting applications.
CT+DIRX1 (X1 COUNTING WITH DIRECTION)
The unit will count one count on every negative edge of the input signal
at Input A. The direction of the count is determined by the logic state of
Input B. A high level at Input B will cause the unit to count in a positive
direction. A low level will cause the unit to count in a negative direction.
The rate display is NOT affected by the logic state of Input B.
CT+DIRX2 (X2 COUNTING WITH DIRECTION)
The unit will count one count on every negative edge of the input signal
and one count on every positive edge of the input signal at Input A. In this
mode, the input signal is effectively doubled. The direction of the count is
determined by the logic state of Input B. A high level at Input B will cause
the unit to count in a positive direction. A low level will cause the unit to
count in a negative direction. The rate display is NOT affected by the state of
Input B.
QUAD X1 (QUADRATURE X1)
Quadrature counting modes are primarily used in positioning and
anti-jitter applications. The reason this mode works is due to the manner in
which the two incoming pulses are positioned relative to each other. The
pulse signal on Input B is shifted 90° away from the pulse signal at Input A.
These two signals are processed by the Legend as follows:
Input A serves as the count and rate input, while Input B serves as
the quadrature input. For quadrature with single edge counting, the
counter will count in a positive direction when Input A is a negative
going edge and Input B is at a low level. The counter will count in a
negative direction when Input A is a positive going edge and Input
B is at a low level. All transitions on Input A are ignored when
Input B is at a high level. These logic rules provide the basis for
anti-jitter operation which will prevent false counts from
occurring due to back-lash, vibration, chatter, etc.
QUAD X2 (QUADRATURE X2)
When two edge counting is used, the quadrature mode works the same as
with single edge counting when Input B is low. But when Input B is a high
level, counts at Input A are no longer ignored. Instead, the logic rules for
Input A are complemented, allowing both edges of Input A to be counted.
This doubles the effective resolution of the encoded input.
QUAD X4 (QUADRATURE X4)
This mode takes the quadrature mode, with two edge counting, one step
further. In quadrature times 4, both Input A and Input B serve as the count
or quadrature input, depending on their state. In one instance, Input A will
serve as the count input and Input B will serve as the quadrature input. In
another instance, Input A will be the quadrature input and Input B will be
the count input. This enables each edge, positive and negative going, of
both inputs, 1 and 2, to be counted. This results in a resolution four times
greater than in the basic quadrature X1 mode. As in the other modes, Input
A is also used for the rate input.
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