Rockwell Automation 1771-VHSC , D17716.5.74 Very High S - Manual (Page 11)

1–3 Overview of the Very High Speed Counter Module
•
counter mode - channel B is tied high or low. Channel A input is
used for pulse. The count is unidirectional with the direction
determined by
channel B.
•
encoder X1 - This is a bidirectional count mode; counting up or
down, using quadrature input signals.
•
encoder X4 - This is a bidirectional count mode, using quadrature
input signals, with 4 times the resolution of X1.
Each of the counters in encoder/counter mode has values associated
with it. These are:
•
preset value
•
rollover value
•
gate/reset input
•
output
Counter Mode
The counter mode allows the module to read incoming pulses and
return them to the programmable controller processor as a binary or
BCD number (0-999,999).
In the counter mode, direction (up counting or down counting) is
determined by the phase B input, which can be a random signal. If
Phase B is high, the counter will count down. If phase B is low or
floating, (that is, not connected), the counter counts up.
If Phase B is: Counter will count (direction):
High Down
Low or floating (not connected) Up
The module reads incoming pulses from a maximum of 4 encoders
(single-ended or differential), counters, pulse generators, mechanical
limit switches, and so forth and returns a count to the programmable
controller processor in a binary or BCD number (0-999,999).