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Special Hardware Requirements:

The S7-200 CPUs can be connected to a PROFIBUS DP network by using an EM 277 PROFIBUS DP expansion module. PROFIBUS stands for “Process Field Bus.” DP stands for “distributed peripherals,” that is, remote I/O. The EM 277 allows the S7-200 CPUs to be DP slave devices on a DP network. A DP master can write data to and read data from the S7-200 CPU over the DP network by using the EM 277 PROFIBUS DP module.

Memory Model DP Master and DP Slave

The purpose of a PROFIBUS DP connection is the exchange of data. A master device writes output data to a slave device. The slave device responds to the write request with input data to be returned to the master.

The master transfers data from an I/O output area to the slave's output buffer (Receive mailbox). The master reads data from the slave's input buffer (Send mailbox) and stores it in an I/O input area. The output and input buffers are located in the CPU's variable memory (V memory) area. The figure below shows the memory model for a transfer of 16 output bytes and 16 input bytes.

PROFIBUS-DP always describes data transfers with respect to the master. Data that is transferred from the master to the slave is always referred to as output data. Data that is transferred from the slave to the master is always referred to as input data. In the slave, data values that come from the master are still referred to as outputs, even though they are inputs to the slave. In the same manner, data values that are returned to the master are still referred to as inputs, even though they are outputs from the slave.

The master tells the slave the start address of the output buffer (Receive mailbox). The master sends the V memory offset of the output buffer to the slave as part of the parameter assignment of the slave. If this offset is zero, the slave will place the output buffer at VB0. If the offset is 5000, the slave will place the output buffer at VB5000.

The master also tells the slave the size of the output buffer (Receive mailbox). The user configures the master to write some number of bytes of data to the slave. The master sends this information to the slave as part of the configuration of the slave. The slave uses this information to set the size of the output buffer. If the master tells the slave that there are 16 output bytes, the slave will set the size of the output buffer to 16 bytes. If the output buffer starts at VB5000, output data from the master will be written to locations VB5000 through VB5015.

The input buffer (Send mailbox, or data to be returned to the master) immediately follows the output buffer. The user also configures the master for the amount of data to be returned by the slave. This value is written to the slave as part of the slave configuration. The slave uses this information to set the size of the input buffer. Continuing with the example above, if the master places the output buffer at VB5000 and sets the size to 16 bytes, the input buffer will begin at VB5016, directly after the output buffer. If the size of the input buffer is also 16 bytes, the input buffer will be placed at VB5016 through VB5031.

After the connection between master and slave has been established, the location of the output buffer and the size of each buffer can be read from the special memory (SM) of the CPU. The following special memory locations describe the first EM 277 module attached to the expansion bus. If the EM 277 is the second intelligent module (non-I/O module), then the SM addresses are offset by 50 (SMB250 to SMB279).

Note that special memory locations 226 through 229 (or 276 through 279) show data written to the EM 277 by the PROFIBUS DP master. Writing to these locations will not change the address or size of the buffers. The EM 277 writes these locations to the CPU whenever there is a change in the PROFIBUS DP status or when the master writes new values to the EM 277.

In STEP 7–Micro/WIN (revision 3.1), to display all of the values described above, click PLC on the menu bar.

On the PLC menu, click Information…. In the Information screen, select an intelligent module, and then click the Intelligent Module Information… button.

Using the EM 277 with a Programming Device or HMI

In addition to acting as a DP slave, the EM 277 can also be used as a programming or HMI port. A programming device can upload or download programs to the CPU that is attached to the EM 277. An HMI device can read data from or write data to the CPU that is attached to the EM 277. The programming device or HMI can be connected to the EM 277 at the same time as a DP master; the DP and programming device/HMI operations do not interfere with each other. To use a programming device or HMI device with an EM 277, the programming device or HMI device must be set up to use MPI or PROFIBUS communications. (The EM 277 will not communicate with a programming device/HMI device that is using PPI protocol.) Use the Setting the PG/PC Interface dialog box to set up communications on the programming device

Setting the DP Address of the EM 277

• Remove power from the CPU and the EM 277.
• Set the rotary switches on the front of the EM 277 to the desired address. The top switch (marked X10) sets the most significant digit of the address (the tens digit). The lower switch (marked X1) sets the least significant digit of the address (the ones digit).
• Apply power to the CPU and the EM 277.

Configuring a DP master

The configuration of a DP master varies considerably depending on the type of device being configured. Tip 57 "How to Connect an S7-300 (Master) to an S7-200 (Slave) by Means of PROFIBUS" describes how to configure a CPU 315-2 DP to communicate with an S7-200 CPU that has an EM 277 PROFIBUS DP module.

General Notes on PROFIBUS DP

                 Contents:

                1.0 General
                2.0 Basic PROFIBUS-DP Functions
                                2.1 Basic Characteristics
                                2.2 System Configuration and Types of Devices 
                                2.3 System Behavior 
                                2.4 Cyclic Data Transmission between the DPM1 and the DP Slaves 
                                2.4.1 Parameter Assignment 
                                2.4.1 Configuration 
                                2.4.1 Data Exchange 
                                2.5 SYNC and FREEZE Mode 
                                2.6 Protection Mechanisms 
                3.0 Extended DP Functions 
                                3.1 DPV1 Extensions 
                                3.2 Other Extensions 
                4.0 Device Database (GSD) Files  

1.0 General

PROFIBUS DP is designed for high-speed data communication at the device level. The protocol and functions are designed according to European Standard EN 50 170. PROFIBUS controllers (programmable logic controllers/PCs) communicate with their distributed field devices (such as I/O, drives, and valves) by means of a high-speed serial link. Most of the data communication with these distributed devices is cyclic. This means that each device is accessed in sequence and the sequence is repeated continuously. Some functions, such as configuration, parameter assignment, diagnostics, and interrupt handling occur outside the normal I/O cycle. These are known as acyclic functions.

2.0 Basic PROFIBUS DPFunctions

The central controller (master) writes data to and reads data from the field devices (slaves). Often this is done at the same time as the program scan of the master controller. The update of all slave devices must be shorter than the program scan time so that the program scan and the I/O update remain synchronized.

2.1 Basic Characteristics

PROFIBUS DP supports high speed data throughput (up to 12 Mbaud). The network has simple installation requirements and uses a proven transmission technology. PROFIBUS provides good diagnostic capabilities and provides for simple service of the network.

• Speed:  PROFIBUS DP requires only about 1 ms at 12 Mbps for the transmission of 2 output bytes and 2 input bytes to each of 32 stations. Figure 1 shows the typical PROFIBUS DP transmission time depending on number of stations and transmission speed. PROFIBUS DP is much faster than corresponding controller functions, such as the XPUT and XGET in the S7-300/S7-400 CPUs, because of the lower overhead associated with the DP communication messages.
• Diagnostic functions:  PROFIBUS DP supports diagnostic functions to determine the location of system faults. The slave devices notify the master that there is a problem or status change when they respond to the normal data exchange message. Once notified, the master immediately sends a diagnostic request to the slave to determine the source of the problem. The diagnostic response messages are divided into three levels:

  Station related diagnostics
  These messages concern the general operational status of the whole device. In the case of the EM 277, the station related diagnostics consist solely of notifying the master that the attached CPU has entered a system fault mode. The EM 277 will return only the station-related diagnostic.

  Module related diagnostics
  These messages indicate that a fault is present in a specific I/O range (for example, an 8-bit output module) of a station. This type of diagnostic is supported by slave devices that control several I/O modules.

  Channel related diagnostics
  These messages indicate an error at an individual input/output bit (such as a short circuit at output 7). This type of diagnostic is supported on slave devices that control a modular I/O system with intelligent modules capable of diagnosing errors.

Test conditions: Each slave has two bytes of input data and two bytes of output data. The minimum slave interval time is 200 µs. TSDI = 37 bit times and TSDR = 11 bit times.

Figure 1: Bus Cycle Time of a PROFIBUS DP Single Master System

2.2 System Configuration and Types of Devices

PROFIBUS DP permits single-master or multiple master systems. Up to 126 devices (master or slaves) can be connected to form a system. The description of the system configuration consists of the number of stations, the assignment between the station address and the I/O addresses, format of the I/O data, format of the diagnostic messages, and the bus parameters used. Each PROFIBUS DP system can contain three different types of devices:

• DP Master Class 1 (DPM1):  The class-1 DP master is a central controller that exchanges information with the slave stations within a specified message cycle. Typical master devices include programmable logic controllers (PLCs) and PC or VME systems.
• DP Master Class 2 (DPM2):  Class-2 DP masters are programming devices, configuration devices, or operator panels. They are used during commissioning for configuration of the DP system or for operation and monitoring purposes. Class-2 masters do not transfer output information to the slave devices. This type of master can only monitor the slave inputs and outputs.
• DP Slave:  A DP slave is a peripheral device (such as an I/O device, a PLC, a drive, an HMI, or a valve) which collects input information and sends that information to the master. Output information from the master is transferred to physical outputs or used by the slave device. There are also devices that supply only input or only output information.

The amount of input and output information depends on the device type. PROFIBUS DP allows a maximum of 246 bytes of input information and 246 bytes of output information to be transmitted within one message. The amount of data transmitted is normally device specific. Many devices support only one or two bytes of data.

The EM 277 PROFIBUS DP module supports several I/O configurations to support a wide range of applications. Different output and input sizes let the transfer of data between the master and the EM 277 match the specific application. The EM 277 writes outputs to an area of V memory in the CPU. This allows the user program to control how the output data is applied. Likewise, input data is read from an area of V memory in the CPU and transferred to the master.

Single Master Systems: In single master systems only one master is active on the bus. Figure 2 shows the system configuration of a single master system. The programmable controller is the central control component (master). The distributed DP slaves are linked by means of the bus to the controller. Single master systems have the shortest bus cycle time.

Figure 2:  PROFIBUS DP Single Master System

Multiple master systems: In multiple master configurations, several masters are connected to a bus. These masters can be independent subsystems, each consisting of the master and its assigned DP slaves, or the other masters can be additional configuration and diagnostic devices as shown in Figure 3. The input and output data of the DP slaves can be read by all DP masters. Only one DP master, the master which configures the slaves, can write outputs to the slaves. Multiple master systems produce a longer bus cycle time than single master systems because of the additional time required to allow the masters to share the same bus.

Figure 3:  PROFIBUS DP Multiple Master System

2.3 System Behavior

System behavior is determined primarily by the operating status of the master. There are three operating states of the PROFIBUS DP network:

• Stop
  In this state, there is no data transmitted between the master and the DP slaves. The master may be in a non-operational state.
• Clear
  In this state, the master reads the input information from the DP slaves and holds the slave outputs in a fail-safe mode. Normally the outputs are set to zero (Clear), but some slave devices allow the definitions of a fail-safe state for the outputs.
• Operate
  In this state, the master writes outputs and reads inputs from all the configured DP slaves.

2.4 Cyclic Data Transmission between the DP Master and the DP Slaves

Data transmission between the master and the DP slaves that are assigned to it is executed automatically by the master in a defined, recurring order. This recurring data transfer is known as a cyclic data transfer. When configuring the system, you specify which DP slaves are assigned to the master and which slaves are to be included or excluded from the cyclic data transfer. Nearly all slaves are set up for a cyclic data transfer.

Data transmission between the master and the DP slave is divided into three phases: parameter assignment, configuration, and data exchange. The first two phases normally occur only once when the system is started or when a slave is added. The data exchange phase is the normal operating mode of the system.

The parameter assignment and configuration information sent to the slaves comes from selections that you made when setting up the system and from the device database files (GSD files) for the slave devices. The GSD files (discussed later) are text files describing the attributes of the slave devices. The system selections and slave attributes are loaded into the DP master, which then uses this information to build the parameter assignment, and configuration messages sent to the slaves.

2.4.1 Parameter Assignment

When the master first enters the Operate state from the Stop state, it must first initialize all of the slave devices by writing the parameter assignment and configuration to the slaves The master first sends a diagnostic request to the slave device. The diagnostic response tells the master the state of the slave, the slave identification number, and whether some other master already controls that slave. The slave identification number is a unique number assigned by the PROFIBUS User Organization to all slaves and masters. The four-digit slave ID number allows the master to verify that the device on the network is the device specified by you during the configuration of the master. If the slave ID does not match your configuration or the slave is already controlled by another master, the master aborts the configuration of the slave and reports an error to you.

If the slave is available, the master sends a parameter assignment message to the slave. The parameter assignment message consists of a few fixed items which configure the slave to match the network parameters (such as watchdog time-outs), and optionally, parameters to configure specific functions or modules within the slave.

The EM 277 accepts only one parameter in addition to the network parameters. This is the V memory offset for the output buffer. If this value is present, the EM 277 uses this offset to access the output buffer and input buffer in the CPU. If the value is not present in the parameter assignment message, the EM 277 assumes that the output buffer starts at VB0 in the CPU.

2.4.2 Configuration

After the parameter assignment message, the master sends the slave a configuration message. This message contains the I/O configuration that the master expects for the slave. Most PROFIBUS devices have a fixed configuration, and for these devices, the writing of the configuration messages is verification that the proper slave device is present. If the configuration is acceptable, the slave is locked to that master address until the master releases it or the slave is power cycled. Only the master that configures a slave is able to enter data exchange mode with that slave.

In the case of the EM 277, the writing of the configuration tells the EM 277 how many output and input bytes the master is requesting the EM 277 and the attached CPU to support. The EM 277 can support several standard configurations (documented in the S7-200 Programmable Controller System Manual and GSD file) and many more optional configurations if the master allows the entering of non-standard configurations. After receiving the configuration message, the EM 277 verifies that the configuration is acceptable and that the output and input buffers will fit within the memory of the attached CPU. If there are no problems with the configuration or parameter assignment message, the EM 277 attaches itself to the master address that sent the configuration messages.

The I/O selection that you defined also selects the data consistency. The data consistency selection tells both the master and the slave how much data to transfer between the network and memory without interruption. PROFIBUS supports three types of consistency: byte, word, and buffer.

• Byte consistency ensures that bytes are transferred as whole units. Byte consistency should be used if all of the bytes within the DP data are independent data items.
• Word consistency ensures that word transfers cannot be interrupted by other processes. Word consistency should be used when the DP data contains integer (two-byte) values. Word consistency forces the master and/or slave to move both bytes of each word between memory and the DP network as a unit that cannot be interrupted or modified by any other process in the CPU.
• Buffer consistency ensures that the entire buffer of data is transferred as a single unit, uninterrupted by any other process. Buffer consistency forces the master and/or slave to move the entire buffer of DP data (all inputs/outputs) between memory and the network without interruption. Buffer consistency should be used when transferring double word values, floating point values or a group of data values which must be acted upon as one unit.

  For example, the EM 277 supports I/O configurations of:
       8 bytes out/ 8 bytes in
       4 word out/ 4 word in
       8-byte buffer I/O

All of these configurations transfer 8 bytes to the EM 277 and 8 bytes back to the master, but the data consistency is different for each configuration. The 8-byte out/in configuration allows user interrupts in the CPU to occur any time during the transfer of the bytes between the EM 277 and the CPU’s V memory. The 4-word out/in configuration allows user interrupts only between words during the transfer, ensuring that the bytes making up the words are not separated during the transfer. The 8 byte buffer I/O configuration causes the CPU to disable user interrupts around the entire transfer of data. The buffer consistency selections in the EM 277 are limited so that the time that user interrupts are disabled does not adversely affect the system.

After a parameter assignment or configuration message has been received, the EM 277 writes the V memory offset and the output and input buffer sizes to the special memory of the CPU, even if the values are not valid for the attached CPU. The DP ERROR LED on the face of the EM 277 will flash red if there is an error in parameter assignment or configuration. If the EM 277 will not enter data exchange mode with the master, you can view the SM locations to help determine where there is a problem.

2.4.3 Data Exchange

After the parameter assignment and configuration messages have been sent to the slave, the master sends another diagnostic request to the slave to determine if the slave has accepted the parameter assignment and configuration messages. If the slave determines that there were errors with the parameter assignment and configuration messages, the master attempts to send these messages to the slave again. If there are no errors in the diagnostic response, the master moves to the next operational phase, data exchange.

Data exchange mode is the normal mode of operation for a DP network. In this mode, the master writes outputs to the slave and the slave returns inputs. If the slave has no outputs, the master still sends a message, but with no output data, and the slave responds with its inputs. If a slave has outputs but no inputs, the slave responds to the output message with a message that contains no data.

The DX MODE LED on the face of the EM 277 is green when the EM 277 is in data exchange mode with the master. The EM 277 is not in data exchange mode if the DX MODE LED is not lit. The DP ERROR LED on the EM 277 is red if the EM 277 was previously in data exchange mode but is not currently in that mode.

The slave sets a diagnostic memory bit in the response if it notes a problem or fault. The diagnostic memory bit causes the master to send a diagnostic request to the slave before transferring any more data to the slave. This allows the master to respond to slave faults promptly.

Figure 4: User Data Transmission with PROFIBUS DP

2.5 SYNC and FREEZE Modes

The master can send control commands to a single slave, a group of slaves, or all slaves simultaneously. These control commands are usually transmitted as broadcast commands that are sent to all slaves simultaneously and acted upon by all slaves if the command was appropriate for the slave. The control commands permit use of SYNC and FREEZE modes for synchronization of the inputs and outputs of the DP slaves.

The master can assign a slave to a group during the parameter assignment phase of startup. The control commands contain a group field in the command. If the group number in the control command matches the group assigned at startup, the slave accepts and acts on the command. If the group numbers do not match, the slave ignores the control command. The master can assign a slave to any one of eight groups, or to no group.

SYNC mode allows the master to synchronize the outputs of a group of slave devices. The slaves begin SYNC mode when they receive a SYNC command from their master. The outputs of all addressed slaves are frozen in their current state. During subsequent user data transmissions from the master, the output data values are accepted and stored by the slaves, but the output states (the physical outputs) remain unchanged. The stored output data are not sent to the outputs until the next SYNC command is received. The SYNC mode allows the master to write output data to the slaves and then have all the slaves assert those outputs at the exact same time when the master broadcasts a SYNC command. SYNC mode is terminated when the master sends an UNSYNC command.

FREEZE mode allows the master to synchronize the inputs of a group of slave devices. The FREEZE mode command causes the addressed slaves to FREEZE their inputs to the current values. The master can now read the frozen input data values from the slaves. The input data values are not updated again until the master sends the next FREEZE command. FREEZE mode is terminated when the master sends the unfreeze command.

The EM 277 supports both the SYNC and FREEZE modes. The EM 277 transfers data to the V memory in the CPU and not to physical I/O, but the concept of SYNC and FREEZE is the same. In SYNC mode, the EM 277 does not transfer new output data to the CPU until a SYNC command is received. In FREEZE mode, the input data that is transferred to the master is not updated until a FREEZE command is received.

2.6 Protection Mechanisms

PROFIBUS DP provides several protection mechanisms to guard against setup errors, data errors, and failure of the transmission equipment.

On the Network

PROFIBUS DP uses an asynchronous communication method with checksums, parity, and redundant data fields to detect errors in the message. The hamming distance of PROFIBUS DP is 4. The hamming distance is a measure of how secure a protocol is against misinterpretation of a packet with errors as a different legal packet. Hamming distance 4 means that at least 4 bits have to be wrong and still match the checksum calculations in order to be mistaken as another valid packet.

At the DP master

The DP master monitors data transmission of the slaves with a timer. A separate timer is used for each slave. This timer expires when correct data transmission does not occur within the specified monitoring interval. This monitoring interval is based on the network configuration,that is, the number of masters, the number of slaves, and the speed of the transmission media. The user is informed when any slave exceeds its time-out.

The master can be set up to take action if any slave fails. If the automatic error reaction (Auto_Clear = True) has been enabled, the master exits the Operate state, switches the outputs of all assigned slaves to fail-safe status, and changes to its Clear state. If this parameter is set to false, the master remains in the Operate state even when a fault occurs, and you specify the system reaction, usually by a special function or user program block.

At the DP slave

The slave uses a watchdog timer to detect failures of the master or the transmission line. If no data communication with the master occurs within the watchdog timer interval, the slave automatically switches its outputs to the fail-safe status.

PROFIBUS provides access protection for the outputs of the DP slaves that operate in multiple master systems. The access protection ensures that only the authorized master can write data and issue control commands to the slave. The authorized master is the master that configured the slave. All other masters can only read the inputs and outputs of a slave, but they cannot write outputs or send control commands.

3.0 Extended DP Functions

PROFIBUS DP has provided extended functions to allow read and write accesses to slaves, interrupt functions and upload or download of data and programs. These extensions are intended for use with more complex PROFIBUS devices that may require parameter changes during normal operation.

The extended DP functions take place in parallel with the normal data exchange cycle. The extended functions are executed at a lower priority than the normal data exchange messages so that the normal DP functions have priority over the extended functions.

The extended DP functions are optional and all slaves need not support them. Existing DP devices that do not want or need to use the new functions can continue to be used since the extended functions are only supplements to already existing functions.

3.1 DPV1 Extensions

The DPV1 extensions are documented in PROFIBUS guideline number 2.082. These extensions allow a master to read and write data to a slave, acknowledge interrupts, and to transfer operational status of the master to the slaves (such as the RUN/STOP status of a programmable logic controller master). The EM 277 does not support any of the DPV1 extensions.

3.2 Other DP Extensions

PROFIBUS supports extensions to allow a transport layer within the PROFIBUS data message. This transport layer is used to support the high-level functions such as the uploading and downloading of programs and data to a slave device. These extensions require the master to set up a connection to the slave device. The master can then communicate to the slave as long as the connection is open. The connection will be closed if either the master or slave detects an error, or if the master or slave fails to communicate within a connection time-out period. If a connection is closed because of error or time-out, the master must re-establish the connection to the slave before communication can continue. The transport layer extensions are device specific and not all PROFIBUS slaves support these extensions.

The EM 277 supports the transport layer extensions to provide all of the functions found in the programming package for the S7-200 CPUs. Through this mechanism, the user can program, debug, and monitor the S7-200 CPU attached to the EM 277. The S7-300 or S7-400 CPUs use these DP extensions to communicate to an S7-200 CPU by means of the GETX and PUTX commands.

The EM 277 supports six connections. One of these connections is reserved for a programming device or PC, and one connection is reserved for an operator panel (i.e. OP7 or TD 200). The remaining four connections are not reserved and can be used by other operator panels, programming devices, or other devices such as an S7-300 CPU. The six DP extension connections are in addition to the normal PROFIBUS DP data exchange function.

The EM 277 can only be used with a programming device that has a CP or MPI communication card. Select the MPI or PROFIBUS Parameter Assignment in the PG/PC interface to allow communication to an EM 277 and S7-200 CPU. The PPI Parameter Assignment cannot be used with an EM 277.

4.0 Device Database Files (GSD Files)

PROFIBUS devices have different performance characteristics. Device features differ in regard to available functionality (such as number of I/O signals and diagnostic messages) or possible bus parameters such as baud rate. These parameters vary individually for each device type and vendor and are usually documented in the technical manual. To achieve a simple Plug and Play configuration of a PROFIBUS network, the characteristic features of a device are specified in an electronic data sheet sometimes called a device database file or GSD file.

The device database files (GSD files) provide a comprehensive description of the characteristics of a device type in a precisely defined format. The GSD files are prepared by the vendor for each type of device and made available to the user in the form of a device database sheet and a device database file. The format of the GSD file permits the configuration system to read in the file of any PROFIBUS DP device and automatically use this information when configuring the system. During the configuration phase, the configuration system automatically performs checks for input errors and consistency of the data entered in relation to the total system.

Figure 5 : Device Databases Permit Open Configuration

The device database file is divided into three parts:

The GSD file is organized as parameter key words followed by the parameter value. Some parameters, such as Vendor_Name, are mandatory; some are optional. The format of the GSD file is designed to be flexible. Some of the entries are lists, like the baud rates supported by a device. Some entries list the input and output configurations of the devices. The GSD file also allows plain text to be assigned to diagnostic information.

GSD files of all PROFIBUS DP devices that have been tested for their conformity to the PROFIBUS standard are available in the GSD library on the Siemens World Wide Web server of the PROFIBUS User Organization for downloading. The address is: http://www.ad.siemens.de/csi_e/gsd

To download the EM 277 GSD file, go to the Siemens internet location http://www.ad.siemens.de/csi_e/gsd and select the PROFIBUS GSD: SIMATIC. GSD library. On the page of SIMATIC downloads, scroll down the page until you find the entry for the EM 277 PROFIBUS DP. From here you can download the GSD file and the bit map files for the EM 277. The GSD file for the is named siem089D.gsd.

For further information, refer to your local PROFIBUS user group. The user groups for each country can be found on the PROFIBUS web site:http://www.profibus.com

Disclaimer

Siemens reserves the right to make changes in these Tips at any time without notice or obligation. Should a conflict arise between the suggestions in these Tips and other Siemens publications such as the S7-200 Programmable Controller System Manual or the SIMATIC S7 / M7 / C7 Programmable Controllers Catalog ST 70, the other publication shall take precedence.