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78 • • • • Chapter Six - Advanced Options
Maximum Query Retries
This is the number of time-outs that must be encountered from a device before the
Server declares the device dead. The default value is 5.
Increasing this value increases the length of time before a device is declared dead.
Decreasing this value causes a device to be declared dead sooner. The tradeoff is that
increasing the value may cause wasted time in scanning devices that are dead, while
decreasing the scan time may cause devices to be declared dead prematurely and
result in error messages.
Dead Device Scan Interval
The Dead Device Scan Interval is the interval in milliseconds at which the Server
will scan a device it has declared dead, to see if it has come back on-line. Reducing
this value devotes more time to scanning dead devices for recovery, which means that
less time is available to scan live devices. Increasing this value means that devices
that may have recovered and come back on-line may not be scanned in time to
respond to a client's request for data.
The default Dead Device Scan Interval is 120,000 milliseconds.
SleepTime For Exception 5
SleepTime For Exception 6
Occasionally, when a power-management device is performing a very processor-
intensive computation, the device will reply to queries from the DDE Server with an
exception code of Acknowledge or Slave Device Busy. These exception codes can
be roughly interpreted as a message from the device saying "Give me a moment to
finish what I'm doing and then I can help you."
The SleepTime for Exception X is the length of time in milliseconds that the Server
will allow a device to complete its tasks before the Server again begins processing
packets addressed to that device. The count begins from the time the Server receives
the exception code.
SleepTime values are supported for Exception Code 5, Acknowledge, and for
Exception Code 6, Slave Device Busy. The default value for both SleepTime
parameters is 1000 milliseconds.
When a device responds with Exception 5, Acknowledge, it is essentially saying "I
have received and accepted the command, now give me some time to go and execute
it." The Server will allow the SleepTime interval to elapse, then send the next packet
addressed to the device.
When a device responds with Exception 6, Slave Device Busy, it is essentially
saying, "I cannot accept any commands now, please ask again later." The Server will
allow the SleepTime interval to elapse, then re-send the same packet to the device.
SleepTime intervals apply only to the device in question. While the Server notes a
device as sleeping, it carries on its business with the remaining devices on the
network without interruption.
TimeDownLoad Period
The PMCS DDE Server performs automatic time synchronization by periodically
sending a time sync message to each device on the network. By default, this message
is sent every 15 minutes (900,000 milliseconds) for the Modbus Concentrator, every
5 seconds for the Modbus Monitor, and every 24 hours for all other devices. This
DDE Server User's Guide
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