Rockwell Automation 1771-VHSC , D17716.5.74 Very High S - Manual (Page 12)

1–4 Overview of the Very High Speed Counter Module
The counter mode accepts only one phase feedback. This
relationship is shown in 1.1.
Figure 1.1
Block Diagram of Counter Mode
From Encoder/Pulse Generator
Phase A
Terminal
Phase B
Terminal
(direction sense)
Gate/Reset
Terminal
1771ĆVHSC
10677ĆI
Encoder Mode
The encoder 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 this mode, the module will accept two phase quadrature feedback.
The module senses the relationship between the 2 phases and counts
up or down accordingly.
Encoder X1 mode uses channel A for the pulse input. With B low
(floating), the count direction is up; when B is high, the count
direction is down.
Encoder X4 mode is identical to X1, except it uses quadrature
signals on channel A and channel B, and counts on the leading and
trailing edges of
A and B.