Siemens SIMATIC NET PROFIBUS, Owner'S Manual

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Configuring Networks
3-31
PROFIBUS Networks SIMATIC NET
6GK1970-5CA20-0AA1 Release 2 05/2000
Calculation of the Slot Time
For the transmission rates of 1.5 Mbps selected in the example, Table 3-9 lists the
following values
a = 351
b = 30
c = 24
On this basis, the slot time is calculated as follows:
Slot time = 351 + (30 x 20) + (24 x 20) = 1431
Entering the Bus Parameters
This means that the following three bus parameters must be entered for the
example:
Slot time (T_slot_Init) = 1431
Retries (Retry_Limit) = 3
Highest station address (HSA) = 126 (default)
These values are entered in STEP 7 in the “Bus Parameters” dialog for the
“User-Defined” bus profile.
You must then trigger the recalculation of the bus parameters with the
“Recalculate” button.