Communication
9.5 Communication using USS
Function Manual
652 Function Manual, 01/2011, 6SL3097-4AB10-0BP3
Character delay time Off time between characters; must be less than 2x character runtime,
but can also be zero
Start delay Off time between USS messages; must be > 2
*
character runtime.
Response delay Processing time of the slave; must be < 20 ms, but larger than the
start delay.
Residual runtime < 1.5
*
(n + 3)
*
character runtime (whereby n = number of data bytes)
"Slave transfer"/
"Master transfer"
Sum of "Start delay", "Response delay" and "Residual runtime"
The master must check the following times:
"Response delay"
Response time of the slave to a USS request
"Residual runtime"
Transmission time of the response telegram sent from the slave
The slave must check the following times:
"Start delay"
Off time between USS messages
"Residual runtime"
Transmission time for a request telegram coming from the master
: : :
: : :
: : :
QFUW
67; /*( $'5 %&&
67; /*( $'5
%&&
FUW FUW
FUW
5HTXHVWIURPWKHPDVWHU
6ODYHUHVSRQVH
6WDUWGHOD\
5HVSRQVHGHOD\
VW QWK
VW
Figure 9-55 Timeout checks on the USS slave
The figure above shows the timeout ranges that have been verified on the USS slave. "crt"
means "Character run time". The maximum range is a factor of 1.5. "Start delay" and
minimum "Response delay" are values that are predefined in the software. The "Residual
runtimes" monitor values that can cause a timeout if they are exceeded on the receipt of
characters.
Process timeouts
Parameter p2040 determines the monitoring time for the received process data via the
fieldbus interface in ms. If no process data is received within this time, message F01910 is
output.
Monitoring is switched off if p2040 = 0.
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