Omron SYSMAC CS Series Operation Manual page 253

Bus Parameters
The parameters to calculate are:
• Min. Slave Interval (
• Target Rotation Time (
• Watchdog timeout (ms)
• Data Control Time (ms)
These four values depend on the number of slave devices allocated to the PROFIBUS Master Unit, the number
of I/O bytes each of the slave devices will exchange with the Master Unit, and how many other Master Units are
on the PROFIBUS network at the same time. Furthermore, the Unit will require additional time to process the
PROFIBUS I/O data and exchange this with the PLC CPU.
Based on this, the Min. Slave Interval value for one Master Unit can be calculated as follows:
Min. Slave Interval = A
in which: A , B , C are constants (in
1 1 1
are constants (in µs) , determining the cycle time between the Unit and the PLC CPU,
A , B , C
2 2 2
slave devices are the devices allocated to this Master Unit only,
modules are the total number of I/O modules, selected for the slave devices.
∑
T = (Min. Slave Interval
TR
The total Target Rotation Time is calculated as the sum of all individual Min. Slave Interval values for each
Master Unit on the PROFIBUS network.
From the total Target Rotation Time the Watchdog time for each slave device is calculated as follows:
T = 3 * T / Baud rate
WD TR
in which: T is the total Target Rotation Time in
TR
Baud rate is the selected baud rate value.
The Watchdog Time value is in turn used to calculate the total Data Control Time:
Data Control Time = 7 * T
Based on measurements, the following values have been determined for the 6 factors in equation [1]:
Baud rate A1
[kBits/s] [t
BIT
9.6 414
19.2 418
45.45 1942
93.75 450
187.5 1390
500 2183
1500 4339
3000 11578
6000 23556
12000 47112
A2: 65.1 µs, B2: 2 µs, C2: 0.5 µs
232
)
t
BIT
)
t
BIT
+ (B * slave devices) + (C
1 1
(bits per µs)*((A
* slave devices) + B
2
determining the PROFIBUS DP cycle time on the bus,
t )
BIT
)
Master
WD
B1 C1
] [t ] [t
BIT BIT
280 11
280 11
361 11
280 11
310 10
310 10
310 11
410 5
800 10
1600 20
* bytes to transfer) +
1
* modules) + (C
2
,
t
BIT
Minimum Min. Slave Interval
] [t ]
BIT
1250
1250
1250
1250
1250
1850
4800
9600
19200
38400
Appendix A
* Words to exchange)[1]
2
[2]
[3]
[4]
[ms]
130
65.1
27.5
13.3
6.67
3.7
3.2
3.2
3.2
3.2