DDE Server User’s Guide
Chapter Six - Advanced Options
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The PMCS DDE Server supports both decimal and hexadecimal address formats.
Select the type of addressing you wish to use (refer to the device user manual if you
are unsure) by clicking either the
Decimal
or
Hexadecimal
radio button. Next, enter
the
Start Address
and
End Address
for the register group in the appropriate boxes.
The PMCS DDE Server supports Modbus RTU extended addressing; in decimal
mode, the range is 0 to 65535; in hexadecimal mode, the address range is 0 to FFFF.
Refer to Appendix A – Register Addressing Conventions for more information on
formatting register addresses.
Next, set the desired polling speed by clicking one of the radio buttons -
Fast Poll
,
Slow Poll
, or
Poll Once
.
The polling speed is based on the scan interval for the topic. A polling speed of
Fast
attempts to scan at the assigned
Scan Interval
. This is the default. Setting the polling
speed to
Slow
causes this register group to be read once every ten scan intervals. This
is typically used for setpoints or low-priority parameters that change infrequently.
Slow Poll is a multiple of
Fast Poll
, with a default value of 10. This multiple is
controlled by a setting in the PMCS DDE Server’s .ini file, and may be changed if
desired. See the section titled PMCS DDE Server .ini File, later in this chapter.
For example, if the scan interval is set to 1000 msec (1 second – this is the default
value), setting the
Poll Speed
to
Fast Poll
causes the Server to scan as close to every
1000 msec as possible (based on the network load, communication bandwidth
availability, etc.); setting the
Poll Speed
to
Slow Poll
reduces the scan attempts to
once every 10,000 msec (10 seconds), or as close to this as possible; i.e.; not less
than 10 seconds (
≥
10,000 msec.)
Poll Once
means that this register group is scanned only the first time data is
requested by a client application. All future requests for the same data receive the
data from this poll. If the device is later declared to be dead, the device is scanned
periodically until it comes back on-line, at which point the
Poll Once
data will be re-
