ProLinx DNPS
♦
ProLinx Gateway
Reference
DNP 3.0 Slave
User Manual
Page 64 of 86
ProSoft Technology, Inc.
December 1, 2009
3.4 DNP
Collision
Avoidance
3.4.1 When
Required
Collision avoidance is required under to following network configurations:
1
A multi-point network is used (that is, master unit is communicating with
several slave units on same physical link). This excludes a dial-up modem
network where the master only communicates with one slave at a time in a
point-to-point physical link. Will only operate on two-wire, half-duplex
communication networks.
2
Unsolicited messaging is used where asynchronous, spontaneous messages
may be generated by any node on the network.
3
Any network where the physical layer does not implement a collision
avoidance scheme and permits several nodes to communicate at one time
(that is, some radio networks).
3.4.2 Rules
RTS controls DCD line on all other units.
No stations transmit while DCD line is high except the one that has the RTS
line high.
After DCD line drops low, slaves wait variable time before attempting to
transmit.
Master has smallest delay (can be set to 0)
Slaves have higher delays (fixed delay (that is, slave#*20 milliseconds) +
random delay (20 to 50 milliseconds))
Only supported in 2-wire half-duplex mode. Not supported in 4-wire half-
duplex mode.
This option is set in the configuration of the module with the port type.
3.4.3 Timing
Chart
Several timing parameters are required for each unit in order to implement the
collision avoidance feature. The parameters are as follows:
Parameter Description
Fixed DCD Idle
Delay Time Before
Transmit
This parameter specifies the minimum number of milliseconds to delay before
transmitting a message after recognizing that the DCD line is low.
Random DCD Idle
Delay Time Before
Transmit
This parameter determines the random time to be added to the above fixed
delay value above before attempting to transmit a message. The value
specified for the parameter determines the range of random values
(milliseconds) to be used. For example, if a value of 20 is specified, the
random delay time will be from 0 to 20 each time the value is requested.
DCD Time Before
Receive
This parameter specifies the number of milliseconds to delay after recognizing
that DCD has been asserted before accepting data. The RTS on time of the
sending unit must be set greater that the time specified here or else the first
part of the data message will be ignored.
RTS On Time
This parameter specifies the number of milliseconds to delay after asserting
the RTS modem control line before sending the data.
RTS Off Time
This parameter specifies the number of milliseconds to delay after the data
has been transmitted before dropping the RTS modem control line.
