MAN1106-07-EN_XL+_UserManual
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9.3.7 HSC Functions
The high-speed input on the XL4 contains many optional tasks. All of which can be disabled, or
set to an internal pre-assigned register (Assigned %Q) or to one of the external high speed
inputs (External Input #1, 2, 3, or 4), or they can be set as an “overflow interrupt” or
“underflow interrupt” meaning that they will occur when either the Overflow or Underflow
input has been activated.
Disable
: When the Disable function is active, it will “disable” the high
-speed inputs and no
longer count pulses until it is re-enabled
Latch: When the Latch function is active, it takes the current value of the Accumulator and
moves it into the “Latch Value” register
Preload: When the pre-
load function is active, it will take the value from the “Preload” register
and put it into the “Accumulator” for the corresponding Counter.
Clear
: When the clear function is active, it will move a value of 0 into the “Accumulator” for
the corresponding counter.
Marker: When the marker function is enabled, it acts as a dynamic enable/disable for the
Disable, Latch, Preload, and Clear functions. I
f the marker is enabled and “Assigned %Q” is
selected, then both the “Disable” and the “Disable Marker” bits need to be set high in order to
disable the high-speed input. If the Marker is set for one of the inputs, then the input will need
to be “High” in order to use any of the Disable,
Clear, Preload, or Latch functions.
9.3.8 Status Bits
There are three status bits (%I registers for each high-speed counter).
Overflow Flag: This status bit turns high when the Accu
mulator “overflows”, it moves from
4,294,967,295 (-
1 if Signed) to 0, this bit can be reset with the “Output Reset Bit”. See Table
12.3.
Underflow Flag
: This status bit turns high when the Accumulator “underflows”, it moves from
0 to 4,294,967,295 (-1 if
Signed), this bit can also be reset with the “Output Reset Bit”.
NOTE: For the Overflow and Underflow flag registers, if using some sort of counter that
counts both up and down, going over the threshold to go negative, triggers the underflow, and
then going back over the threshold back into positive numbers will trigger the positive
register to go active.
High Speed Out: This register will follow the high-speed output assigned to the counter, it is
important to note that this register is still populated within the scan time so the value in this
register may not be up to date depending on the timing of the output (it should be up to date
within one scan).
