Allen-Bradley POINT I/O 1734-VHSC24, User Manual, Page: 13 / 64

Publication 1734-UM003A-EN-P - August 2000
About the Very High Speed Counter Modules 1-5
X4 Multiplying Encoder Mode
Quadrature input signals are used to count on leading AND trailing
edges of A AND B for a bidirectional count, and channel B is used to
determine the direction.
[ B = leads A, Count = Down; B = follows A, Count = Up ]
Period/Rate Mode
The Period/Rate Mode will return an incoming frequency and a total
accumulated count to the PointBus, by gating an internal 5MHz
internal clock with an external signal.
This mode determines the frequency and total number of input pulses
by counting the number of internal 5MHz clock pulses over a
user-specified number of input signal pulses. At the end of the
specified number of pulses, the module returns the frequency (0 -
1MHz). When the frequency is updated, both outputs are checked
against their associated presets.
EXAMPLE
Example of Period/Rate Mode
A ( Not Used )
B ( Not Used )
Encoder / Pulse Generator
1734-VHSC
Input A
Input B
Z Input ( Pulse )
5 MHz Internal
(Gate / Reset )
Input Z
Z
Accumulated Count
1
Scalar
5 MHz Clk
Sampling Clock
Assumes symmetrical pulse, 50% duty cycle, so Period = Sample Time On X 2 {On & Off}
10 20
Frequency = 1 / Period If Count = 20, Scalar = 1, and Clock Period = ( 1 / 5 MHz )
Frequency = 1 / [ ( 20 / 1 ) X ( 1 / 5 MHz ) X 2 ] = 125 kHz
Frequency & Outputs
Updated Here