Siemens SIMATIC S7-400H Manual page 67

9. The recommended value for the max. blocking time for priority classes > 15
now results from:
T
P15 =
]
Example of calculation of T
In the following the maximum permissible period of time on update during which
the operating system performs no program scanning and no I/O updates is
determined for a given system configuration.
There are 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 module.
1. From the bus parameters in STEP 7:
T
TR_1
T
TR_2
T
DP_UM_1
T
DP_UM_2
2. From the Technical Data for the DP slaves used:
T
SLAVE_UM_1
T
SLAVE_UM_2
3. From the technological specifications for your system:
T
PTO_1
T
PTO_2
4. From the user program:
T = 300 ms
WA
T
PROG
5. From formula [1]:
T (DP master system_1)
P15
= 1250 ms – (2
T (DP master system_2)
P15
= 1200 ms – (2
Check: if T
6. T
P15_HW
7. From formula [2]:
T
P15_OD
Check: if T
S7-400H Programmable Controller Fault-Tolerant Systems
A5E00068197-04
MAX (T , T
P15_AWP P15_OD
P15
= 25 ms
= 30 ms
= 100 ms
= 80 ms
= 30 ms
= 50 ms
= 1250 ms
= 1200 ms
= 50 ms
25 ms + 300 ms + 50 ms + 100 ms + 30 ms) = 720 ms
30 ms + 300 ms + 50 ms + 80 ms + 50 ms) = 660 ms
> 0, continue with
P15
= MIN (720 ms, 660 ms) = 660 ms
= 50 ms + T = 50 ms + 90 ms = 140 ms
PH
= 140 ms < T
P15_OD
)
= 660 ms, continue with
P15_HW
Link-up and Update
[3
5-23