Rockwell Automation 1755-OF8 GuardPLC Controller Systems - Manual (Page 158)

158 Publication 1753-UM001C-EN-P - March 2010
Chapter 16 Peer-to-peer Communication Overview
The ResponseTime is the sum of the following variables, described in
the table below.
ResponseTime = T
GR1
+ T
1
+ T
GR2
+ T
3
+ T
2
Receive Timeout (ReceiveTMO)
ReceiveTMO is the safety-related, user-configurable monitoring time,
within which PES
1
must receive a correct response from PES
2
.
If ReceiveTMO elapses, safety-related communication closes down
and all imported (via communication) safety-related tags reset to their
user-configurable initial values.
If the ReceiveTMO
≥
2 x ResponseTime(minimum), the loss of at least
one message can be handled without losing the Peer-to-Peer
connection.
Response Time Variables
Variable Definition
T
GR1
Message delay between two PES:
CPU
1
→
COM
1
→
network
→
COM
2
→
CPU
2
T
1
Time on CPU
2
to process all protocol stacks:
T
1
= CycleTime(CPU
2
) x n
2
where n
2
is the number of cycles needed on CPU
2
to process all protocol
stacks. Set the Communication Time Slice (see below) large enough to allow
all protocol stacks to be processed in one cycle.
T
2
Delay of the acknowledgement on CPU
2
:
T
2
= AckTMO + n
2
x [0 … CycleTime(CPU
2
)]
If AckTMO = 0 or ProdRate = 0, then T
2
= 0
T
GR2
Message delay between two PES:
CPU
2
→
COM
2
→
network
→
COM
1
→
CPU
1
(usually identical with T
GR1
)
T
3
Time on CPU
1
to process all protocol stacks:
T
3
= CycleTime(CPU
1
) x n
1
where n
1
is the number of cycles needed on CPU
1
to process all protocol
stacks. Set Communication Time Slice (see page 176 ) large enough to allow
all protocol stacks to be processed in one cycle.
TIP
ReceiveTMO is also valid for the return path from PES
2
to PES
1
.