Equidistant PROFIBUS
Equidistant (isochronous) PROFIBUS forms the basis for synchronized processing cycles.
The PROFIBUS system provides a basic clock for this. The "isochrone mode" system property can couple a S7-400-CPU with the equidistant PROFIBUS.
Isochronous data processing
Data is processed isochronously using the following method:
• Reading of the input data is synchronized with the DP cycle; all the input data is read at the same time.
• The user program that processes the data is synchronized with the DP cycle by means of the isochronous interrupt OBs OB61 to OB64.
• Data output is synchronized with the DP cycle; All the output data takes effect at the same time.
• All input and output data is transferred consistently. This means that all the data from the process image belongs together, both logically and with respect to timing.
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Figure 5-8 Isochronous data processing
TDP System cycle
Ti Time at which the input data is read
To Time at which the output data is output
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PROFIBUS DP 5.1 CPU 41x as DP master / DP slave
Synchronization of the cycles allows the input data to be read with a cycle "n-1", the data to be transferred and processed with cycle "n", and the calculated output data to be transferred and switched to the "terminals" at the start of cycle "n+1". This gives a true process response time from "Ti + TDP + To" to "Ti + (2 x TDP) + To".
The "isochrone mode" system property means that cycle times within the S7-400 system are constant; the S7-400 system is strictly deterministic on the bus system.
Just-In-Time
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The fast and reliable response time of a system operating in isochrone mode is based on the fact that all data is provided just-in-time. The equidistant (isochronous) DP cycle forms the master clock for this.
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PROFIBUS DP
5.1 CPU 41x as DP master / DP slave
S7-400 Automation System, CPU Specifications
5-30 Manual, 11/2006, A5E00850746-02
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Figure 5-10 System cycle
The start of the I/O read cycle is started one bias time Ti earlier in order to make all input data available for transfer on the DP subnet at the start of the next DP cycle. You can configure this bias time Ti yourself or have it determined automatically by STEP 7.
PROFIBUS transfers the input data to the DP master via the DP subnet. The synchronous cycle interrupt OB (OB61, OB62, OB63 or OB64) is called. The user program in the synchronous cycle interrupt OB determines the process response and provides the output data in time for the start of the next DP cycle. You can configure the length of the DP cycle yourself or have it determined automatically by STEP 7.
The output data is provided just-in-time for the start of the next DP cycle. The data is transferred on the DP subnet to the DP slaves and passed to the process in an isochronous operation, that is, in synchronism with the time To.
The result is a total reproducible response time of "Ti + (2 x TDP) + To" for the transfer from the input to the output terminal.
Characteristics of isochrone mode
Isochrone mode is characterized by the three following essential features:
• The user program is synchronized with I/O processing, that is, all operations are coordinated on a time basis. All input data is logged at a defined time. The output data also takes effect at a defined time. The I/O data is synchronized with the system clock cycle up to the terminals. The data of one cycle is always processed in the next cycle, and it takes effect at the terminals in the subsequent cycle.
• I/O data is processed in equidistant (isochrone) mode, that is, input data is always read at constant intervals, and always output at the same intervals.
• All I/O data is transferred consistently, that is, all the data of a process image belongs together logically and has the same timing.
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PROFIBUS DP 5.1 CPU 41x as DP master / DP slave
Direct access in isochrone mode Caution
Avoid direct access (e.g. T PAB) to I/O areas that you process with SFC 127. Ignoring this rule may mean that the write operation fails.
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PROFIBUS DP
5.1 CPU 41x as DP master / DP slave
S7-400 Automation System, CPU Specifications
5-32 Manual, 11/2006, A5E00850746-02
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PROFINET 6
6.1
6.1Introduction
What is PROFINET?
PROFINET is the open, non-proprietary Industrial Ethernet standard for automation It enables comprehensive communication from the business management level down to the field level.
PROFINET fulfills the high demands of industry, for example;
• Industrial-compliant installation engineering
• Real-time capability
• Non-proprietary engineering
There are a wide range of products from active and passive network components,
controllers, distributed field devices to components for industrial wireless LAN and industrial security available for PROFINET.
Documentation on the Internet:
You will find numerous documents about PROFINET at the web site at http://www.profibus.com.
Further information can be found at the web site " http://www.siemens.com/profinet/.
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PROFINET
6.2 PROFINET IO and PROFINET CBA
S7-400 Automation System, CPU Specifications
6-2 Manual, 11/2006, A5E00850746-02