Rockwell Automation 1771-VHSC , D17716.5.74 Very High S - Manual (Page 22)

1–14 Overview of the Very High Speed Counter Module
Sample Period
You can set the sample period used in the frequency calculation in
the rate measurement mode. Allowable values are 10 milliseconds to
2 seconds in 10 millisecond increments. The default value is 1
second. (Note: A 0 in the BTW initialization word is equivalent to
the default value of 1 second.)
The sample period is set in words 21 through 24 of the BTW
initialization file (chapter 4).
Connection to Counter Inputs
The only user connections used in the rate measurement mode are to
phase A of the module. The gate/reset and channel B terminals are
not used in this mode.
The VHSC module has 8 outputs, isolated in groups of 2. Each of
the outputs is capable of sourcing current and will operate between 5
and 24 volts dc. You must connect an external power supply to each
of the outputs. The outputs can source 2 amps dc. The outputs are
hardware-driven and will turn on in less than 10
µ
sec when the
appropriate count value has been reached.
Enabling and Forcing Outputs
Outputs may be forced on or off independent of count or frequency
value. To force the outputs, they must first be enabled. Enabling the
outputs is done through a data table word 2, bits 0-7 in the BTW
initialization file (chapter 4). Once the outputs have been enabled,
they may be forced on by setting bits 8-15 in word 2 of the BTW
initialization file. The outputs can be forced off by setting the enable
bit to 0.
Assigning Outputs to Counters
By setting bits in the block transfer write initialization file, you can
assign the outputs on the module to any of the various counters. You
can assign as many as 8 outputs to a given counter. However, an
output may be assigned only once to a counter--it is not possible to
use the same output with 2 different counters. Refer to words 25, 30,
35, 40, 45, 50, 55, 60 of the BTW initialization file in chapter 4.
Outputs