Siemens SIMATIC NET PROFIBUS manual Calculation of the Slot Time, Entering the Bus Parameters

Configuring Networks

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.

PROFIBUS Networks SIMATIC NET	3-31
6GK1970-5CA20-0AA1 Release 2 05/2000