within a given amount of time. For example, a baud rate of 19.2 kbaud describes a transmission rate of 19,200 bits per second.
Every device that communicates over a given network must be configured to transmit data at the same baud rate. Therefore, the fastest baud rate for the network is determined by the slowest device connected to the network. Table 7-1 lists the baud rates supported by the S7-200.
Table 7-1 Baud Rates Supported by the S7-200 Network Standard Network Using an EM 277 Freeport Mode Baud Rate 9.6 kbaud to 187.5 kbaud 9.6 kbaud to 12 Mbaud 1200 baud to 115.2 kbaud The network address is a unique number that you assign to each device on the network. The unique network address ensures that the data is transferred to or retrieved from the correct device. The S7-200 supports network addresses from 0 to 126. For an S7-200 with two ports, each port has a network address. Table 7-2 lists the default (factory) settings for the S7-200 devices.
Table 7-2 Default Addresses for S7-200 Devices S7-200 Device STEP 7--Micro/WIN HMI (TD 200, TP, or OP) S7-200 CPU Setting the Baud Rate and Network Address for STEP 7--Micro/WIN
You must configure the baud rate and network address for STEP 7--Micro/WIN. The baud rate must be the same as the other devices on the network, and the network address must be unique.
Typically, you do not change the network address (0) for STEP 7--Micro/WIN. If your network includes another programming package, you might need to change the network address for STEP 7--Micro/WIN.
As shown in Figure 7-3, configuring the baud rate and network address for STEP 7--Micro/WIN is simple. After you click the Communications icon in the Navigation bar, you perform the following steps:
1. Double-click the icon in the Communications Setup window. 2. Click the Properties button on the Set PG/PC Interface dialog box. 3. Select the network address for STEP 7--Micro/WIN. 4. Select the baud rate for STEP 7--Micro/WIN.
Default Address 0 1 2
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Figure 7-3 Configuring STEP 7--Micro/WIN
Setting the Baud Rate and Network Address for the S7-200
You must also configure the baud rate and network address for the S7-200. The system block of the S7-200 stores the baud rate and network address. After you select the parameters for the S7-200, you must download the system block to the S7-200.
The default baud rate for each S7-200 port is 9.6 kbaud, and the default network address is 2.
As shown in Figure 7-4, use STEP 7--Micro/WIN to set the baud rate and network address for the S7-200. After you select the System Block icon in the Navigation bar or select the View > Component > System Block menu command, you perform the following steps:
1. Select the network address for the S7-200. 2. Select the baud rate for the S7-200. 3. Download the system block to the S7-200.
4 3 2 1
Figure 7-4 Configuring the S7-200 CPU
Tip
1 2 Selection of all baud rate options is permitted. STEP 7--Micro/WIN validates this selection during the download of the System Block. Baud rate selections that would prevent STEP 7--Micro/WIN from communicating with the S7-200 are prevented from being downloaded. Setting the Remote Address
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Before you can download the updated settings to the S7-200, you must set both the communications (COM) port of STEP 7--Micro/WIN (local) and the address of the S7-200 (remote) to match the current setting of the remote S7-200. See Figure 7-5.
After you download the updated settings, you may need to reconfigure the PG/PC Interface baud rate setting (if different from the setting used when downloading to the remote S7-200). Refer to Figure 7-3 to configure the baud rate.
Figure 7-5 Configuring STEP 7--Micro/WIN
Searching for the S7-200 CPUs on a Network
You can search for and identify the S7-200 CPUs that are attached to your network. You can also search the network at a specific baud rate or at all baud rates when looking for S7-200s.
Only PPI Multi-Master cables permit searching of all baud rates. This feature is not available if communicating through a CP card. The search starts at the baud rate that is currently selected.
1. Open the Communications dialog box and double-click the Refresh icon to start the search. 2. To search all baud rates, select the Search All Baud Rates check box. 2. Selecting the Communications Protocol for Your Network
The following information is an overview of the protocols supported by the S7-200 CPUs. 1. Point-to-Point Interface (PPI) 2. Multi-Point Interface (MPI) 3. PROFIBUS
Figure 7-6 Searching for CPUs on a Network
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Based on the Open System Interconnection (OSI) seven-layer model of communications architecture, these protocols are implemented on a token ring network which conforms to the PROFIBUS standard as defined in the European Standard EN 50170. These protocols are asynchronous, character-based protocols with one start bit, eight data bits, even parity, and one stop bit. Communications frames depend upon special start and stop characters, source and destination station addresses, frame length, and a checksum for data integrity. The protocols can run on a network simultaneously without interfering with each other, as long as the baud rate is the same for each protocol.
Ethernet is also available for the S7-200 CPU with expansion modules CP243--1 and CP243--1 IT. PPI Protocol
PPI is a master-slave protocol: the master devices send requests to the slave devices, and the slave devices respond. See Figure 7-7. Slave devices do not initiate messages, but wait until a master sends them a request or polls them for a response.
Masters communicate to slaves by means of a shared connection which is managed by the PPI protocol. PPI does not limit the number of masters that can communicate with any one slave; however, you cannot install more than 32 masters on the network.
Figure 7-7 PPI Network
S7-200 CPUs can act as master devices while they are in RUN mode, if you enable PPI master mode in the user program. (See the description of SMB30 in Appendix D.) After enabling PPI master mode, you can use the Network Read or the Network Write instructions to read from or write to other S7-200s.
While the S7-200 is acting as a PPI master, it still responds as a slave to requests from other masters. PPI Advanced allows network devices to establish a logical connection between the devices. With PPI Advanced, there are a limited number of connections supplied by each device. See Table 7-3 for the number of connections supported by the S7-200.
All S7-200 CPUs support both PPI and PPI Advanced protocols, while PPI Advanced is the only PPI protocol supported by the EM 277 module.
Table 7-3 Number of Connections for the S7-200 CPU and EM 277 Modules Module S7-200 CPU Port 0 Port 1 Baud Rate 9.6 kbaud, 19.2 kbaud, or 187.5 kbaud 9.6 kbaud, 19.2 kbaud, or 187.5 kbaud EM 277 Module
Connections 4 4 6 per module 9.6 kbaud to 12 Mbaud 14
MPI Protocol
MPI allows both master-master and master-slave communications. See Figure 7-8. To communicate with an S7-200 CPU, STEP 7--Micro/WIN establishes a master--slave connection. MPI protocol does not communicate with an S7-200 CPU operating as a master.
Network devices communicate by means of separate connections (managed by the MPI protocol) between any two devices. Communication between devices is limited to the number of connections supported by the S7-200 CPU or EM 277 modules. See Table 7-3 for the number of connections supported by the S7-200.
For MPI protocol, the S7-300 and S7-400 PLCs use the XGET and XPUT instructions to read and write data to the S7-200 CPU. For information about these instructions, refer to your S7-300 or S7-400 programming manual.
Figure 7-8 MPI Network
PROFIBUS Protocol
The PROFIBUS protocol is designed for high-speed communications with distributed I/O devices (remote I/O). There are many PROFIBUS devices available from a variety of manufacturers. These devices range from simple input or output modules to motor controllers and PLCs.
PROFIBUS networks typically have one master and several slave I/O devices. See Figure 7-9. The master device is configured to know what types of I/O slaves are connected and at what addresses. The master initializes the network and verifies that the slave devices on the network match the configuration. The master continuously writes output data to the slaves and reads input data from them.
Figure 7-9 PROFIBUS Network
When a DP master configures a slave device successfully, it then owns that slave device. If there is a second master device on the network, it has very limited access to the slaves owned by the first master.
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TCP/IP Protocol
The S7-200 can support TCP/IP Ethernet communication through the use of an Ethernet (CP 243--1) orInternet (CP 243--1 IT) expansion module. Table 7-4 shows the baud rate and number of connections supported by these modules.
Table 7-4 Number of Connections for the Ethernet (CP 243--1) and the Internet (CP 243--1 IT) Modules Module Ethernet (CP 243--1) Module Internet (CP 243--1 IT) Module 10 to 100 Mbaud Baud Rate Connections 8 general purpose connections 1 STEP 7--Micro/WIN connection Refer to the CP 243--1 Communications Processor for Industrial Ethernet Manual or the CP 243--1 IT Communications Processor for Industrial Ethernet and Information Technology Manual for additional information.
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