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6/22/2016 Tip 56: General Notes about PROFIBUS and EM 277

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Version 5.0. Updated 10/01

General Notes about PROFIBUS and EM 277 (Tip 56)

Category: CommunicationsSpecial Hardware Requirements:

One SIMATIC S7-200 CPU 222, CPU 224, CPU 226, or CPU 226XMOne EM 277 PROFIBUS DP expansion module

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The S7-200 CPUs can be connected to a PROFIBUS DP network by using an EM 277 PROFIBUS DP expansionmodule. PROFIBUS stands for Process Field Bus. DP stands for distributed peripherals, that is, remote I/O. The EM277 allows the S7-200 CPUs to be DP slave devices on a DP network. A DP master can write data to and read datafrom 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 slavedevice. 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 datafrom 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 bytesand 16 input bytes.

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


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The master tells the slave the start address of the output buffer (Receive mailbox). The master sends the V memoryoffset of the output buffer to the slave as part of the parameter assignment of the slave. If this offset is zero, the slavewill 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 writesome number of bytes of data to the slave. The master sends this information to the slave as part of the configuration ofthe slave. The slave uses this information to set the size of the output buffer. If the master tells the slave that there are16 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 alsoconfigures the master for the amount of data to be returned by the slave. This value is written to the slave as part of theslave configuration. The slave uses this information to set the size of the input buffer. Continuing with the exampleabove, if the master places the output buffer at VB5000 and sets the size to 16 bytes, the input buffer will begin atVB5016, directly after the output buffer. If the size of the input buffer is also 16 bytes, the input buffer will be placed atVB5016 through VB5031.

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

SMB200 to 215 These locations contain 16 ASCII characters giving the module name.

SMB216 to 219 These locations contain the software revision of the EM 277. The first two characters are themajor revision and the second two characters are the minor revision. For example: if SMB216-219contain 0102, the software revision is 1.02.

SMW220 This is the EM 277 module error status. Only two values are currently defined. A zero in thislocation means that there are no errors. A value of one means that there is no user supplied 24VDC power attached to the module.

SMB222 This is the address of the EM 277 that is read from the switches.

SMB224 This byte location contains the status of the PROFIBUS DP connection. The user program shouldmonitor this location so that the program knows if the DP connection is operating properly. If there


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is an error (any value except 2), the program can take action based on the failure of the DPconnection. The following status values are defined:

0 = No DP communication has occurred since the EM 277 was powered on.1 = The DP master is communicating to the EM 277 but there is a problem with the configuration orparameter assignment information sent by the master.2 = The EM 277 and the DP master are currently exchanging data (normal operation).3 = The EM 277 and the DP master are not currently exchanging data but were exchanging data inthe past.

SMB225 This byte contains the address of the master that configured the EM 277. This is the master that is

able to write outputs and read the inputs of the slave.

SMW226 This word contains the V memory address of the output buffer (Receive mailbox). This value iswritten to the slave in a parameter assignment message during the initialization of the connection.

SMB228 This byte contains the size of the output buffer (size of the Receive mailbox in bytes). This value iswritten to the slave in a configuration message during the initialization of the connection.

SMB229 This byte contains the size of the input buffer (size of the Send mailbox in bytes). This value iswritten to the slave in a configuration message during the initialization of the connection.

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

In STEP 7Micro/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 theIntelligent 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 devicecan upload or download programs to the CPU that is attached to the EM 277. An HMI device can read data from or writedata to the CPU that is attached to the EM 277. The programming device or HMI can be connected to the EM 277 at thesame time as a DP master the DP and programming device/HMI operations do not interfere with each other. To use aprogramming device or HMI device with an EM 277, the programming device or HMI device must be set up to use MPI orPROFIBUS communications. (The EM 277 will not communicate with a programming device/HMI device that is usingPPI 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) setsthe most significant digit of the address (the tens digit). The lower switch (marked X1) sets the least significantdigit of the address (the ones digit).

Apply power to the CPU and the EM 277.

Note that the address switches on the EM 277 are only read when the EM 277 is powered on. Changing the addressswitches on the EM 277 with power applied has no effect until the next power cycle.

Configuring a DP master

The configuration of a DP master varies considerably depending on the type of device being configured. Tip 57 "How toConnect an S7-300 (Master) to an S7-200 (Slave) by Means of PROFIBUS" describes how to configure a CPU 315-2 DPto 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


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2.2 System Configuration and Types of Devices2.3 System Behavior2.4 Cyclic Data Transmission between the DPM1 and the DP Slaves2.4.1 Parameter Assignment2.4.1 Configuration2.4.1 Data Exchange2.5 SYNC and FREEZE Mode2.6 Protection Mechanisms

3.0 Extended DP Functions3.1 DPV1 Extensions

3.2 Other Extensions4.0 Device Database (GSD) Files

1.0 General

PROFIBUS DP is designed for high-speed data communication at the device level. The protocol and functions aredesigned 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 insequence 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 thesame time as the program scan of the master controller. The update of all slave devices must be shorter than theprogram 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 requirementsand uses a proven transmission technology. PROFIBUS provides good diagnostic capabilities and provides for simpleservice of the network.

Speed: PROFIBUS DP requires only about 1 ms at 12 Mbps for the transmission of 2 output bytes and 2 inputbytes to each of 32 stations. Figure 1 shows the typical PROFIBUS DP transmission time depending on numberof stations and transmission speed. PROFIBUS DP is much faster than corresponding controller functions, suchas 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 dataexchange message. Once notified, the master immediately sends a diagnostic request to the slave to determinethe source of the problem. The diagnostic response messages are divided into three levels:

Station related diagnosticsThese messages concern the general operational status of the whole device. In the case of the EM277, the station related diagnostics consist solely of notifying the master that the attached CPU hasentered a system fault mode. The EM 277 will return only the station-related diagnostic.

Module related diagnosticsThese 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/Omodules.

Channel related diagnosticsThese messages indicate an error at an individual input/output bit (such as a short circuit at output7). This type of diagnostic is supported on slave devices that control a modular I/O system withintelligent modules capable of diagnosing errors.


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Test conditions: Each slave has two bytes of input data and two bytes of output data. The minimum slave interval time is200 s. 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 beconnected to form a system. The description of the system configuration consists of the number of stations, theassignment between the station address and the I/O addresses, format of the I/O data, format of the diagnosticmessages, 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 theslave 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 operatorpanels. They are used during commissioning for configuration of the DP system or for operation and monitoringpurposes. Class-2 masters do not transfer output information to the slave devices. This type of master can onlymonitor 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) whichcollects input information and sends that information to the master. Output information from the master istransferred to physical outputs or used by the slave device. There are also devices that supply only input or onlyoutput information.

The amount of input and output information depends on the device type. PROFIBUS DP allows a maximum of 246 bytesof input information and 246 bytes of output information to be transmitted within one message. The amount of datatransmitted 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. Differentoutput and input sizes let the transfer of data between the master and the EM 277 match the specific application. The EM277 writes outputs to an area of V memory in the CPU. This allows the user program to control how the output data isapplied. 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 systemconfiguration of a single master system. The programmable controller is the central control component (master). Thedistributed DP slaves are linked by means of the bus to the controller. Single master systems have the shortest buscycle time.


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Figure 2: PROFIBUS DP Single Master System

Multiple master systems: In multiple master configurations, several masters are connected to a bus. These masters canbe independent subsystems, each consisting of the master and its assigned DP slaves, or the other masters can beadditional configuration and diagnostic devices as shown in Figure 3. The input and output data of the DP slaves can beread 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 thePROFIBUS DP network:

StopIn this state, there is no data transmitted between the master and the DP slaves. The master may be in a non-operational state.ClearIn this state, the master reads the input information from the DP slaves and holds the slave outputs in a fail-safemode. Normally the outputs are set to zero (Clear), but some slave devices allow the definitions of a fail-safe statefor the outputs.OperateIn 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 masterin a defined, recurring order. This recurring data transfer is known as a cyclic data transfer. When configuring the system,


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you specify which DP slaves are assigned to the master and which slaves are to be included or excluded from the cyclicdata 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 aslave 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 whensetting up the system and from the device database files (GSD files) for the slave devices. The GSD files (discussedlater) are text files describing the attributes of the slave devices. The system selections and slave attributes are loadedinto the DP master, which then uses this information to build the parameter assignment, and configuration messages sentto 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 bywriting the parameter assignment and configuration to the slaves The master first sends a diagnostic request to the slavedevice. The diagnostic response tells the master the state of the slave, the slave identification number, and whethersome other master already controls that slave. The slave identification number is a unique number assigned by thePROFIBUS User Organization to all slaves and masters. The four-digit slave ID number allows the master to verify thatthe device on the network is the device specified by you during the configuration of the master. If the slave ID does notmatch your configuration or the slave is already controlled by another master, the master aborts the configuration of theslave and reports an error to you.

If the slave is available, the master sends a parameter assignment message to the slave. The parameter assignmentmessage consists of a few fixed items which configure the slave to match the network parameters (such as watchdogtime-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 outputbuffer. If this value is present, the EM 277 uses this offset to access the output buffer and input buffer in the CPU. If thevalue is not present in the parameter assignment message, the EM 277 assumes that the output buffer starts at VB0 inthe CPU.

2.4.2 Configuration

After the parameter assignment message, the master sends the slave a configuration message. This message containsthe I/O configuration that the master expects for the slave. Most PROFIBUS devices have a fixed configuration, and forthese 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 powercycled. 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 masteris 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 optionalconfigurations 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 ofthe attached CPU. If there are no problems with the configuration or parameter assignment message, the EM 277attaches 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 masterand the slave how much data to transfer between the network and memory without interruption. PROFIBUS supportsthree 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 thebytes within the DP data are independent data items.Word consistency ensures that word transfers cannot be interrupted by other processes. Word consistencyshould be used when the DP data contains integer (two-byte) values. Word consistency forces the master and/orslave to move both bytes of each word between memory and the DP network as a unit that cannot be interruptedor 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 otherprocess. Buffer consistency forces the master and/or slave to move the entire buffer of DP data (allinputs/outputs) between memory and the network without interruption. Buffer consistency should be used whentransferring double word values, floating point values or a group of data values which must be acted upon as oneunit.

For example, the EM 277 supports I/O configurations of:


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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 isdifferent for each configuration. The 8-byte out/in configuration allows user interrupts in the CPU to occur any time duringthe transfer of the bytes between the EM 277 and the CPUs V memory. The 4-word out/in configuration allows userinterrupts only between words during the transfer, ensuring that the bytes making up the words are not separated duringthe transfer. The 8 byte buffer I/O configuration causes the CPU to disable user interrupts around the entire transfer ofdata. The buffer consistency selections in the EM 277 are limited so that the time that user interrupts are disabled doesnot adversely affect the system.

After a parameter assignment or configuration message has been received, the EM 277 writes the V memory offset andthe output and input buffer sizes to the special memory of the CPU, even if the values are not valid for the attachedCPU. The DP ERROR LED on the face of the EM 277 will flash red if there is an error in parameter assignment orconfiguration. If the EM 277 will not enter data exchange mode with the master, you can view the SM locations to helpdetermine 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 anotherdiagnostic request to the slave to determine if the slave has accepted the parameter assignment and configurationmessages. If the slave determines that there were errors with the parameter assignment and configuration messages, themaster attempts to send these messages to the slave again. If there are no errors in the diagnostic response, the mastermoves 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 theslave 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 messagewith 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. TheEM 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 theEM 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 causesthe master to send a diagnostic request to the slave before transferring any more data to the slave. This allows themaster 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 controlcommands are usually transmitted as broadcast commands that are sent to all slaves simultaneously and acted upon byall slaves if the command was appropriate for the slave. The control commands permit use of SYNC and FREEZEmodes for synchronization of the inputs and outputs of the DP slaves.


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The master can assign a slave to a group during the parameter assignment phase of startup. The control commandscontain 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 modewhen they receive a SYNC command from their master. The outputs of all addressed slaves are frozen in their currentstate. During subsequent user data transmissions from the master, the output data values are accepted and stored by theslaves, but the output states (the physical outputs) remain unchanged. The stored output data are not sent to the outputsuntil the next SYNC command is received. The SYNC mode allows the master to write output data to the slaves andthen 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 commandcauses the addressed slaves to FREEZE their inputs to the current values. The master can now read the frozen inputdata values from the slaves. The input data values are not updated again until the master sends the next FREEZEcommand. 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 andnot to physical I/O, but the concept of SYNC and FREEZE is the same. In SYNC mode, the EM 277 does not transfernew output data to the CPU until a SYNC command is received. In FREEZE mode, the input data that is transferred tothe 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 thetransmission equipment.

On the Network

PROFIBUS DP uses an asynchronous communication method with checksums, parity, and redundant data fields todetect errors in the message. The hamming distance of PROFIBUS DP is 4. The hamming distance is a measure of howsecure a protocol is against misinterpretation of a packet with errors as a different legal packet. Hamming distance 4means that at least 4 bits have to be wrong and still match the checksum calculations in order to be mistaken as anothervalid 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 timerexpires when correct data transmission does not occur within the specified monitoring interval. This monitoring interval isbased on the network configuration,that is, the number of masters, the number of slaves, and the speed of thetransmission 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 beenenabled, the master exits the Operate state, switches the outputs of all assigned slaves to fail-safe status, and changesto its Clear state. If this parameter is set to false, the master remains in the Operate state even when a fault occurs, andyou 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 withthe 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. Theaccess protection ensures that only the authorized master can write data and issue control commands to the slave. Theauthorized master is the master that configured the slave. All other masters can only read the inputs and outputs of aslave, 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 andupload or download of data and programs. These extensions are intended for use with more complex PROFIBUS devicesthat may require parameter changes during normal operation.

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


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the extended functions.

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

3.1 DPV1 Extensions

The DPV1 extensions are documented in PROFIBUS guideline number 2.082. These extensions allow a master to readand write data to a slave, acknowledge interrupts, and to transfer operational status of the master to the slaves (such asthe 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 isused 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 theslave as long as the connection is open. The connection will be closed if either the master or slave detects an error, or ifthe master or slave fails to communicate within a connection time-out period. If a connection is closed because of error ortime-out, the master must re-establish the connection to the slave before communication can continue. The transportlayer 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 forthe 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 theGETX and PUTX commands.

The EM 277 supports six connections. One of these connections is reserved for a programming device or PC, and oneconnection is reserved for an operator panel (i.e. OP7 or TD 200). The remaining four connections are not reserved andcan be used by other operator panels, programming devices, or other devices such as an S7-300 CPU. The six DPextension 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 orPROFIBUS Parameter Assignment in the PG/PC interface to allow communication to an EM 277 and S7-200 CPU. ThePPI 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. Theseparameters vary individually for each device type and vendor and are usually documented in the technical manual. Toachieve a simple Plug and Play configuration of a PROFIBUS network, the characteristic features of a device arespecified 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 aprecisely defined format. The GSD files are prepared by the vendor for each type of device and made available to theuser in the form of a device database sheet and a device database file. The format of the GSD file permits theconfiguration system to read in the file of any PROFIBUS DP device and automatically use this information whenconfiguring the system. During the configuration phase, the configuration system automatically performs checks for inputerrors and consistency of the data entered in relation to the total system.


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Figure 5 : Device Databases Permit Open Configuration

The device database file is divided into three parts:

General specificationsThis section contains vendor and device names, hardware and software release information, baud rates supported,features supported, and network timing information.DP master related specificationsThis section contains all parameters which only apply to DP master devices, such as the maximum number ofslaves which can be connected, or upload and download capabilities. This section does not exist for slavedevices.DP slave-related specificationsThis section contains all specifications related to slaves, such as the number and type of I/O channels,specification of diagnostic tests, and information on the consistency of the I/O data.

The GSD file is organized as parameter key words followed by the parameter value. Some parameters, such asVendor_Name, are mandatory some are optional. The format of the GSD file is designed to be flexible. Some of theentries 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 areavailable in the GSD library on the Siemens World Wide Web server of the PROFIBUS User Organization fordownloading. 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 selectthe PROFIBUS GSD: SIMATIC. GSD library. On the page of SIMATIC downloads, scroll down the page until you findthe 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 thePROFIBUS web site: http://www.profibus.com

DisclaimerThese SIMATIC S7-200 Application Tips are provided free of charge to give users of the S7-200 examples ofprogramming techniques available to accomplish certain tasks in various applications. These Tips do not purport to coverall details or variations in equipment, nor do they provide for every possible contingency. Your application may be differentfrom those described herein. It is your responsibility to use the SIMATIC S7-200 properly in your application. These Tipsdo not relieve you of the responsibility to use sound practices in application, installation, operation and maintenance. Byusing these Tips, you acknowledge that Siemens shall not be liable under any theory for damages or personal injuryresulting from such use.

Siemens reserves the right to make changes in these Tips at any time without notice or obligation. Should a conflict arisebetween the suggestions in these Tips and other Siemens publications such as the S7-200 Programmable ControllerSystem Manual or the SIMATIC S7 / M7 / C7 Programmable Controllers Catalog ST 70, the other publication shall takeprecedence.
http://www.profibus.com/http://www.ad.siemens.de/csi_e/gsdhttp://www.ad.siemens.de/csi_e/gsd


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Copyright 2002 Siemens Energy & Automation

SIMATIC S7-200 customers have free use of the application tips. These tips are only a general approach to using the S7-200 with various applications. Yourspecific application may be different. It is your responsibility to use the SIMATIC S7-200 properly in your applications.