Help on Projecting

For getting an overview over the bus load, a few information are displayed in this section, with this information it is easier to configure a PROFINET IO system optimally.

The PROFINET IO frame has a minimal length of 80 bytes (44 bytes overhead and 36 bytes minimum user data). That means an extension of this frame size takes only place if the sum of the process data (respectively divided in input and output data) is greater than 36 Byte.

In the following figure this is pointed up again: The first 2 examples (CI501-PNIO alone and CI502-PNIO with 5 expansion modules DC532) will fit into the minimum frame size. In the third example, only two expansion modules AX522 are used on an CI501-PNIO but that suffices to get above the minimum frame size.

Effect of the process data length on the frame length

Note

For better overview, the data length of the CRC, which follows the user data, is included into the overhead.

The following tables show the length of the process data of all available S500 PROFINET IO devices and of all S500 expansion modules. With these tables and the aid of the following formula, it is possible to calculate the frame time for a modular IO device (separately for input and output data).

Module type	Input data length [bytes]	Output data length [bytes]
CD522	24	32
CI501-PNIO	9	5
CI502-PNIO	2	2
CI504-PNIO	0 … 36	0 … 36
CI506-PNIO	0 … 36	0 … 36

Length of the process data of the S500 \ I/O Modules:

Module type	Input data length [bytes]	Output data length [bytes]
DA501	12	8
DC522	2	2
DC523	3	3
DC532	4	2
DC561	2	2
DI524	4	0
DI561	1	0
DI562	2	0
DI571	1	0
DO561	0	1
DO571	0	1
DO572	0	1
DX522	1	1
DX531	1	1
DX561	1	1
DX571	1	1
AI523	32	0
AI531	32	1
AI561	8	0
AI562	4	0
AI563	8	0
AO523	0	32
AO561	0	4
AX521	8	8
AX522	16	16
AX561	8	4

t:sub:input = Max(6.4 µs, (SUM_input + 44) * 0.08 µs) / ReductionRatio

t:sub:output = Max(6.4 µs, (SUM_output + 44) * 0.08 µs) / ReductionRatio

t:sub:sum = t_input + t_output

Note

For CI506-PNIO the IO Data size of connected CANOPEN slaves must also be considered.

With these values, an estimation of the expected bus load is possible. Afterwards, all frame times of input and output must be added. The result is the average time the complete communication needs. In the following table this is done for an example application for getting a sense of the expected times. The sum of the frame times of the different IO devices is here 130.3 µs, that means with a basic cycle time of 1 ms the bus load is only 13.26 % and that means there is enough reserve for NRT data transfer for other network applications.

Device	DAP	EXP1	EXP2	EXP3	EXP4	EXP5	EXP6	EXP7	Send Clock Factor [ms]	Reduction Ratio	Time [µs]
1	CI501-PNIO	DC532	AX521						1	1	12.8
2	CI501-PNIO	DC532	AX521						1	2	6.4
3	CI501-PNIO	DC532	AX521						1	4	3.2
4	CI501-PNIO	DC532	AX521						1	8	1.6
5	CI501-PNIO	DC532	DC532	DC532	DC532				1	1	12.8
6	CI501-PNIO	DC532	DC532	DC532	DC532				1	2	6.4
7	CI501-PNIO	DC532	DC532	DC532	DC532				1	4	3.2
8	CI501-PNIO	DC532	DC532	DC532	DC532				1	8	1.6
9	CI501-PNIO	DC532	DC532	DC532	DC532	AX522	AX522	AX522	1	1	17.8
10	CI501-PNIO	DC532	DC532	DC532	DC532	AX522	AX522	AX522	1	2	8.9
11	CI501-PNIO	DC532	DC532	DC532	DC532	AX522	AX522	AX522	1	4	4.4
12	CI501-PNIO	DC532	DC532	DC532	DC532	AX522	AX522	AX522	1	8	2.2
13	CI501-PNIO	AX522	AX522	AX522	AX522	AX522	AX522	AX522	1	1	26.1
14	CI501-PNIO	AX522	AX522	AX522	AX522	AX522	AX522	AX522	1	2	13.0
15	CI501-PNIO	AX522	AX522	AX522	AX522	AX522	AX522	AX522	1	4	6.6
16	CI501-PNIO	AX522	AX522	AX522	AX522	AX522	AX522	AX522	1	8	3.3
										TOTAL	130.3