Analysis of Siemens S7-200 SMART communication port connection technology

Each S7-200 SMART CPU provides an Ethernet port and an RS485 port (port 0). The standard CPU additionally supports the SB CM01 signal board (port 1). The signal board can be configured as an RS232 communication port or an RS485 communication port through STEP 7-Micro/WIN SMART software.

CPU Communication Port Pinout

1. The RS485 communication port (port 0) integrated in the S7-200 SMART CPU is a 9-pin D-type connector compatible with RS485. The pin assignment of the RS485 communication port integrated in the CPU is shown in Table 1. Pin assignment of the RS485 port integrated in the S7-200 SMART CPU.

Table 1. Pin assignment of the integrated RS485 port of the S7-200 SMART CPU

2. The standard CPU additionally supports the SB CM01 signal board, which can be configured as an RS485 communication port or an RS232 communication port through the STEP 7-Micro/WIN SMART software. Table 2 shows the pin assignment of the SB CM01 signal board.

Table 2. Pin assignment for the S7-200 SMART SB CM01 signal board port (port 1)

The process of using STEP 7-Micro/WIN SMART software to configure the SB CM01 signal board as an RS485 communication port or an RS232 communication port is shown in Figure 1. SB CM01 signal board configuration process.

Figure 1. SB CM01 signal board configuration process

EM DP01 communication port pin assignment

The RS485 serial communication interface on the EM DP01 is an RS485 compatible nine-pin mini D-type socket, which is consistent with the PROFIBUS standard specified by the European standard EN 50170. The following figure introduces the pin assignment of the communication port.

Figure 2. Pin assignment of the S7-200SMART EM DP01 communication port

Ethernet port connection

The Ethernet port of the S7-200 SMART CPU has two network connection methods: direct connection and network connection.

Direct connection:

When an S7-200 SMART CPU communicates with a programming device, HMI or another S7-200 SMART CPU, a direct connection is achieved. A direct connection does not require a switch, and the two devices can be directly connected using a network cable, as shown in Figure 2. Direct connection of communication devices.

Figure 3. Direct connection of communication devices

Network connection:

When more than two communication devices communicate, a switch is required to achieve network connection. You can use the rail-mounted Siemens CSM1277 4-port switch to connect multiple CPUs and HMI devices, as shown in Figure 3. Network connection of multiple communication devices.

Figure 4. Network connection of multiple communication devices

RS485 network connection

Transmission distance and baud rate of RS485 network

RS485 network is a linear bus network using shielded twisted pair cables, and terminal resistors are required at both ends of the bus. RS485 network allows a maximum of 32 communication nodes per segment, and the maximum cable length allowed is determined by two factors, whether the communication port is isolated and the communication baud rate, as shown in Table 3. Maximum length of RS485 segment cable.

Table 3. Maximum length of RS485 segment cables

The RS485 port integrated in the S7-200 SMART CPU and the SB CM01 signal board are non-isolated communication ports, and the maximum communication distance allowed is 50m, which is the distance from the first communication node to the last node in the network segment. If the number of communication nodes in the network is greater than 32 or the communication distance is greater than 50m, you need to add an RS485 repeater to expand the network connection.

Notice:

● The RS485 port integrated in the S7-200 SMART CPU and the SB CM01 signal board are non-isolated. When communicating with other nodes in the network segment, it is necessary to make an equipotential connection of the reference point potential or use an RS485 repeater to provide isolation for the network. Communication between nodes with different reference point potentials may cause communication errors or port burnout.

● When the S7-200 SAMRT CPU is networked with other nodes, the M terminal of the sensor power supply at the lower right corner of the CPU module can be connected to the 0V reference point of the communication port of other nodes to achieve equipotential connection.

RS485 Repeater

RS485 repeaters can be used to extend network distances, electrically isolate different network segments, and increase the number of communication nodes. The functions of repeaters are as follows:

1. Extend the network distance:

Adding a repeater to the network allows the network to be extended by another 50m. If two repeaters are connected together without other nodes in between, the network can be extended by 1000m. A maximum of 9 Siemens repeaters can be used in a network. See Figure 4. Network extension using RS485 repeaters.

Figure 5. Using RS485 repeaters to expand the network

Notice:

When using S7-200 SMART CPU free port communication, Modbus RTU communication, and USS communication, Siemens repeaters cannot be used to expand the network.

2. Electrically isolate different network segments:

Isolation networks can isolate network segments with different reference point potentials from each other, thereby ensuring the quality of communication transmission.

3. Add network equipment:

In one RS485 network segment, up to 32 communication nodes can be connected. Using a repeater can expand a network segment to connect 32 more communication nodes, but the repeater itself also occupies a communication node position, so the expanded network segment can only connect 31 more communication nodes.

RS485 Network Connector

Siemens provides two types of RS485 network connectors (as shown in Figure 5. RS485 network connector), which can be used to easily connect multiple communication nodes to the communication network. One is a standard network connector, and the other has a programmable interface. The network connector with a programmable interface can expand all the communication pins of the RS485 port integrated in the S7-200 SMART CPU to the programming interface, where pins 2 and 7 provide 24VDC power to the outside, which can be used to connect TD400C.

Figure 6. RS485 network connector

The two sets of connection terminals on the network connector are used to connect the input cable and the output cable. The network connector has a selection switch for the terminal and bias resistor. The communication nodes at both ends of the network must set the selection switch of the network connector to On, and the communication nodes in the middle of the network need to set the selection switch to Off. The typical network connector terminal resistor and bias resistor wiring are shown in Table 4. Network connector terminal and bias resistor.

Table 4. Network Connector Termination and Bias Resistors

The SB CM01 signal board can be used to connect the RS485 network. When the signal board is a terminal communication node, it is necessary to connect the terminal resistor and the bias resistor. The typical circuit diagram is shown in Figure 6. SB CM01 signal board terminal and bias resistor wiring diagram.

Figure 7. SB CM01 signal board terminals and bias resistor wiring

Notice:

● Terminal resistance is used to eliminate signal reflection caused by discontinuous characteristic impedance in communication cables. When the signal is transmitted to the end of the network, if the cable impedance is very small or there is no impedance, signal reflection will be caused at this place. The method to eliminate this reflection is to terminate a terminal resistor with the same characteristic impedance as the cable at both ends of the network to make the cable impedance continuous.

● When there is no communication node sending data on the network, the network bus is in an idle state. Adding a bias resistor can create a certain idle potential on the bus, ensuring the stability of the logic signals "0" and "1".

RS232 Connection

RS232 network is a point-to-point connection between two devices, with a maximum communication distance of 15m and a maximum communication rate of 115.2 Kbit/s. RS232 connection can be used to connect scanners, printers, modems and other devices. The SB CM01 signal board can be configured as an RS232 communication port. The typical RS232 wiring method is shown in Figure 7. SB CM01 signal board RS232 connection diagram.

Multiple communication modes of S7-200Smart

1. Two S7-200Smart wireless communication

2. Kingview/wincc/touch screen as master station communicates with S7-200smart slave station

3. S7-200Smart is used as the master station, and the two slave stations collect 4 analog signals and 4 switch signals respectively.

4. Siemens touch screen and S7-200SMART Ethernet wireless communication

5. Wireless PROFINET communication between S7-200 SMART and IO modules

6. Wireless Ethernet communication between Weiluntong touch screen and S7-200Smart