Allen-Bradley A-B QUALITY DL20 Series User Manual page 175

PLC Output /
DL20 Input Signals
You will need to configure the parallel port to communicate with the input
converter and determine the timing for data transfers between the DL20 and
the converter.
Use the instructions below to set up the DL20 parallel port for operation with
Series A, B, C or later Parallel Input Converters.
1. Select the AC input mode of the parallel port when programming the
DL20. You can do this by accessing the special function Set Up I/O Ports
and answering appropriately to the prompt USE NG 1/2 SER A,B?
Answering Yes to this prompt selects an AC sampling method.
Answering No selects a DC sampling method.
2. Select a scan rate of 28 (default) for AC sampling with Parallel Input
Converters (Catalog No. 2706-NG1, -NG2 Series A, B, C or later). The
scan rate is used to determine the minimum amount of time that stable
data must be present on the input terminals of the AC converter to allow
for two samples of the parallel port.
3. If the Parallel Input Converter (Catalog No. 2706-NG1, -NG2 Series C or
later) is used, the debounce value must also be specified. Use the value of
25 ms for the debounce.
Minimum Data Hold Times (MDHT) values listed below are based on a scan
rate of 28.
Series A or B Converter MDHT = 180 ms
Series C and Later Converter MDHT = 100 ms
The following diagram shows the relationship between Minimum Data Hold
Times (MDHT) and Minimum Time Between Messages (MTBM).
5 - 30VDC
0VDC
Appendix H
Parallel Input Converter
Timing Diagram
Start of Message 1
MDHT
MTBM
Start of Message 2
H–3