Siemens SIMATIC NET PROFIBUS manual Constants for calculating the slot time at DP standard

Configuration					6.2 Configuration of redundant optical rings
Data rate		a	b	c
12	MBit/s 1)	1651	240	28
6	MBit/s 1)	951	120	24
3	MBit/s 1)	551	60	24
1.5	MBit/s	351	30	24
500	kBit/s	251	10	24
187.5	kBit/s	171	3.75	24
93.75 kBit/s		171	1.875	24
45.45 kBit/s		851	0.909	24
19.2	kBit/s	171	0.384	24
9.6	kBit/s	171	0.192	24
Table 3a: Constants for calculating the slot time at DP standard
(redundant optical ring)
Data rate		a	b	c
12	MBit/s 1)	1651	240	28
6	MBit/s 1)	951	120	24
3	MBit/s 1)	551	60	24
1.5	MBit/s	2011	30	24
500	kBit/s	771	10	24
187.5	kBit/s	771	3.75	24
93.75 kBit/s		451	1.875	24
45.45 kBit/s		851	0.909	24
19.2	kBit/s	181	0.384	24
9.6	kBit/s	171	0.192	24

Table 3b: Constants for calculating the slot time at DP/FMS (”universal“) and DP with S5 95U (redundant optical ring)

The calculation of the slot time only takes into consideration the optical network and the connection of bus sub- scribers to the OLM via an RS 485 bus segment with a respctive length of max. 20 m. Longer RS 485 bus segments must be allowed for by adding them to the Length OF .

Note:

When the slot time is configured with a too small value the OLM will, through it’s fault function and fault indications, indicate such. The System-LED will blink red/green.

1)Using the OLM/G11-1300 and OLM/G12-1300 at data rates of 12 MBit/s, 6 MBit/s, 3 MBit/s and 1.5 MBit/s the minimum slot times according to the following table must be met.

Data rate		Minimum slot time
12	MBit/s	3800 tBit
6	MBit/s	2000 tBit
3	MBit/s	1000 tBit
1.5 MBit/s		530 tBit

Table 4: Minimum slot time on OLM/G11-1300 and

OLM/G12-1300

Use the values from Table 4 if the calculated slot time is smaller than the minimum slot time indicated in the table.

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