Rockwell Automation PLC-5 Fieldbus Solutions for Integrated Architecture User Manual - Manual (Page 92)

Publication 1757-UM006A-EN-P - May 2002
4-6 Configurating the 1757-FIM
System Management Timers
T1, T2, and T3 are the System Management Timers. The units are
1/32000 of a second, so 96000 gets 3 seconds.
T1
T1 specifies how long the 1788-CN2FF waits for an answer to a
System Management message, such as Set PD Tag.
The time needs to include the time to acquire the Token for
Unscheduled Transmission, transmit the message, remote node to
process the message, remote node to acquire Token, transmit reply.
Depending on the Function Block execution and Publishing schedule,
this might take as little as 100 mS, but 3 seconds is recommended by
the FF, and it doesn't hurt to allow extra time for slow nodes or slow
commands.
T2
T2 specifies how long a Remote Node, such as a Pressure Transmitter
waits for the next System Management message in a series of System
Management messages until it concludes that the System Manager has
failed. This is used for SET_ADDRESS sequence as shown in the
following diagram.
As you can see, to set a node's address requires several messages to
be sent from the System Manager (the CN2FF in our case) to a node. If
the System Manager fails before completing all the steps, the Remote
Node must give up and resume operation at its previous settings. The
time for the remote node to wait after each step is called T2.
T3
Specifies how long after a node is changed to a new address it might
take for it to begin communication at the new address.
This time includes stuff like writing the new information to flash
memory and re-initializing some stuff, but is primarily the time it takes
for the Link Active Scheduler (LAS), the CN2FF in this case, to Probe
the Node at its new address.