Allen-Bradley A-B QUALITY DL20 Series User Manual page 82

Chapter 7
The Parallel Port
Time Driven Sampling
Because it does not require an additional ETS rising or falling edge to read
DL20 data lines, time-driven sampling is the recommended way of looking at
DL20 data lines. When time-driven sampling is selected, the DL20 looks at
the data lines periodically. The time interval used by the DL20 is set using
the special functions menu described in Chapter 8.
Time-Driven Sampling Methods
AC and DC sampling can be used. Both sampling methods reduce false
message triggering and invalid data. When DC sampling is selected, you can
select the debounce time (see Chapter 8).
AC sampling is required when using a Parallel Input Converter (Catalog No.
2706-NG1, -NG2 Series A or B).
DC sampling is required when using a Parallel Input Converter (Catalog No.
2706-NG1, -NG2 Series C or later). These converters convert the AC signal
to DC.
AC Sampling
The DL20 uses a special AC sampling method when AC sampling is chosen
and the Series A or B Parallel Input Converters are used. See Appendix H
for more information.
Data Hold Time
For AC data input to be recognized on the parallel port, it must be present
and unchanging for a minimum of 180ms (Series A and B Parallel Input
Converters).
AC Sampling Restrictions
The frequency of AC is approximately 60 Hz. The voltage must fall within
the range of 108-132 VRMS. The AC on all inputs must be in phase.
Note: The AC power input used to power the device does not need to be in
phase with the AC on the parallel port inputs. A Parallel Input Converter
(Catalog No. 2706-NG1, -NG2) is required for AC parallel inputs.
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