Siemens SIMATIC S7-400H System Manual page 113

Example of the calculation of T
In the next steps, we take an existing configuration and we define the maximum permitted
time during an update during which the operating system does not execute any programs or
update the I/O.
We assume two DP master systems: DP master system_1 is "connected" to the CPU via the
MPI/DP interface of the CPU, and DP master system_2 via an external DP master interface.
1. Based on the bus parameters in STEP 7:
2. Based on the technical data of the DP slaves used:
3. Based on the technological demands of your system:
4. Based on the user program:
5. Based on the formula [1]:
Check: since T
1. T
2. Based on the formula [2]:
T
P15_OD
Check: since T
1. Based on section 7.4.4 with 170 KB of user program data:
Check: as T
1. Based on formula [3], we now obtain the recommended maximum disable time for priority
T
P15
T
P15
This means that by setting a maximum disable time of 194 ms for priority classes > 15 in
STEP 7, you can ensure that any signal changes during the update are detected with a
signal duration of 1250 ms or 1200 ms.
S7-400H
System Manual, 09/2007, A5E00267695-03
P15
T = 25 ms
TR_1
T = 30 ms
TR_2
T = 100 ms
DP_UM_1
T = 80 ms
DP_UM_2
T = 30 ms
SLAVE_UM_1
T = 50 ms
SLAVE_UM_2
T = 1250 ms
PTO_1
T = 1200 ms
PTO_2
T = 300 ms
WA
T = 50 ms
PROG
T (DP master system_1)
P15
= 1250 ms - (2 x 25 ms + 300 ms + 50 ms + 100 ms + 30 ms) = 720 ms
T (DP master system_2)
P15
= 1200 ms - (2 x 30 ms + 300 ms + 50 ms + 80 ms + 50 ms) = 660 ms
> 0, continue with
P15
= MIN (720 ms, 660 ms) = 660 ms
P15_HW
= 50 ms + T = 50 ms + 90 ms = 140 ms
PH
= 140 ms < T
P15_OD
T = 194 ms
P15_AWP
= 194 ms < T
P15_AWP
classes > 15:
= MAX (194 ms, 140 ms)
= 194 ms
= 660 ms continue with
P15_HW
= 660 ms continue with
P15_HW
Link-up and update
9.4 Time monitoring
113