Schneider TSX17 serial communication upgrade and replacement

Schneider TSX17 serial communication upgrade and replacement

Introduction: Communication Challenges of the Old TSX 17 Micro PLC

Among numerous industrial systems that have been in service for over 20 years, Schneider Electric's TSX 17 series micro PLCs still undertake important control tasks. These devices have compact structures and high reliability, especially suitable for small automation equipment, packaging machinery, specialized machine tools, and other scenarios. However, over time, users are facing two tricky issues:

Communication module shutdown: Key components such as TSX SCG 1131 (RS232 serial port module), TSX SCG 1161 (UNI-TELWAY bus module), and TSX 17 ACC5 adapter are no longer in production, and original spare parts are almost extinct.

Difficulty in integrating with upper level systems: Old systems only support RS232 or UNI-TELWAY dedicated buses, while modern monitoring systems commonly use open protocols such as Ethernet/IP, Profinet, Modbus TCP, making data acquisition and remote control extremely difficult.

For factories that rely on TSX 17, completely replacing the entire control system is costly and carries significant risks. Therefore, a more realistic strategy is to have a deep understanding of the working principles and configuration methods of existing communication modules, master troubleshooting techniques, and, when necessary, perform "precise replacement" through second-hand markets or protocol conversion technologies.

This article will focus on the two core communication solutions of TSX 17 series - asynchronous serial communication (RS232) and UNI-TELWAY fieldbus, providing a complete set of technical references from hardware functions, software configuration, master-slave communication mechanism, troubleshooting to upgrade and replacement paths.

Asynchronous Serial Communication Module TSX SCG 1131

2.1 Module positioning and basic characteristics

TSX SCG 1131 is a single channel asynchronous serial communication module for TSX 17-20 micro PLC, mainly used for exchanging data with external devices with RS232C interface. Typical applications include:

Connect to the upper monitoring computer (SCADA)

Connect a serial printer or barcode scanner

Connecting a modem for remote maintenance

Communicate with other PLCs or smart meters

Electrical interface: RS232C, full duplex (capable of simultaneous transmission and reception), character transmission. The maximum transmission distance is limited by the RS232 standard (usually within 15 meters), but can be extended through a modem.

Data exchange capability: Each frame can transmit up to 30 bytes, suitable for application scenarios of medium to short data packets (such as recipe download, status reading, alarm reporting).

2.2 Programmable configuration of communication parameters

All communication parameters of TSX SCG 1131 are programmed through PL7-2 software (with specific language card: TSX P17 20 FC2/FD2), rather than through hardware dip switches. This brings flexibility, but also requires engineers to be clear about the meaning of each parameter.

Configuration process: Users need to send an 8-word configuration table through the Text Function Block at the beginning of the program. Each word (Word) in the table defines the following parameters in code form:

Parameter optional range description

Function specifies the channel operation mode or transmission protocol such as character mode, Modbus, etc

Data bit length of 7 or 8 bits defines character format

Parity check: No parity check, odd parity check, even parity check are used for error detection

Stop bit 1 or 2 is used for character spacing

Baud rate 150~19200 bps standard rate, does not support higher rates

Send echo enable/disable, wait for echo after sending, timeout triggers error

Receive echo enable/disable. Immediately send back the received characters as they are online

Engineering Tip: When communicating with a PC serial port, typically 8 data bits, no parity check, 1 stop bit, 9600 or 19200 bps are used. The echo function is generally disabled unless a specific handshake protocol is required.

2.3 Transmission/reception dialogue mechanism

After configuration is complete, users perform data exchange by programming text blocks and assigning request codes. The supported request types include:

Sending with timeout (can be paired with confirmation): suitable for scenarios where it is necessary to ensure that the other party receives it

Sending without timeout/confirmation: broadcast style one-way communication

Receive with timeout: wait for a specified number of characters, abort upon timeout

Unconfirmed reception: continuous reception without returning confirmation

Sending/receiving combination: Half duplex response communication (such as inquiry response)

Each frame of data has a maximum of 30 characters. In practical projects, multiple frames are often concatenated to achieve longer data transmission, but the application needs to manage frame segmentation and reassembly.

2.4 Operation monitoring and command control

The module provides Status Words for the PLC program to read and confirm the communication status. Common status indicators include:

Tx Active: Sending in progress

Rx Buffer Full: The receive buffer is full

Timeout: timeout occurred

Parity Error: Parity check error

Frame Error: Frame format error

In addition, Command Words can be used for proactive intervention:

Force switch to fallback position

Suspend the ongoing exchange

This is very useful when dealing with communication deadlocks or device exceptions. For example, when the slave does not respond, the current request is terminated through a command word and the communication line is reset.

Modbus/Jbus protocol support

Both TSX SCG 1131 and TSX SCG 1161 modules support Modbus/Jbus protocol, which is one of the de facto standards in the field of industrial automation.

3.1 Master and Slave Modes

The module can be configured as a master or slave:

Master station mode: initiates communication requests proactively, reads or writes data from other slave station devices (such as frequency converters, instruments, HMI).

Slave mode: passively responding to requests from the master station, commonly used to integrate TSX 17 as a sub device into larger monitoring systems.

When configured in half duplex character mode, the module can also directly handle custom protocols, but Modbus is more standardized.

3.2 Data exchange process

Within the PLC, data tables are exchanged between the PLC and modules through text blocks, and the modules are responsible for converting this data into Modbus/Jbus messages. This process is transparent to PLC programmers: just fill the data to be sent into the specified table, then call the text function block, and the module will automatically complete the protocol encapsulation.

Typical application: TSX 17 serves as a slave station, providing current production, fault codes, temperature values, etc. to the upper computer; Or as a master station, read the values of multiple Modbus instruments.

Note: In Modbus/Jbus mode, the data length of one frame is also limited by 30 bytes, but more data can be obtained by reading multiple frames (such as reading multiple registers with function code 03).

UNI-TELWAY bus connection

UNI-TELWAY is an early fieldbus introduced by Schneider Electric, which is based on master-slave or token mechanism and supports multi station communication. TSX 17 can be connected to UNI-TELWAY in two ways:

4.1 Method 1: Using the TSX 17 ACC5 adapter module

Connection path: Terminal Port of TSX 17 → TSX 17 ACC5 → UNI-TELWAY bus

Role limitation: At this time, TSX 17 can only act as a slave and cannot initiate communication proactively.

Applicable scenario: Simply from the station device, such as only reporting data without reading from other stations.

4.2 Method 2: Through TSX SCG 1161 communication module

Connection path: Insert TSX SCG 1161 into the I/O bus expansion slot of the PLC → Connect cable through TSX CSC 015 → TSX SCA 62 user socket on UNI-TELWAY bus

Flexible role: TSX 17 can serve as a master or slave.

Key points of hard connection: When making a "T-shaped tap" on the UNI-TELWAY bus, a dedicated dual channel user socket TSX SCA 62 must be used, and wires cannot be directly connected in parallel.

4.3 Server and Client Mode

In the UNI-TELWAY network, TSX 17 can simultaneously act as both a server and a client:

Server: receives service requests from other clients in the network (such as reading/writing internal variables, starting/stopping PLC), executes them, and returns a confirmation. The client requests access through UNI-TE.

Client: Actively sends requests to other servers, such as reading data from remote stations, writing commands, or remotely controlling RUN/STOP. This requires the use of text function blocks to construct requests.

This bidirectional capability allows TSX 17 to serve as both a data acquisition station and a control master station, adapting to complex network topologies.

Attention: Regardless of which method is used to connect UNI-TELWAY, TSX 17 must be equipped with the corresponding version of PL7-2 language card:

Connected through ACC5: requires TSX P17 20 FA/FB/FC2/FD2

Connected through SCG 1161: requires TSX P17 20 FC2/FD2

PL7-2 Software Configuration Detailed Explanation (Practical Steps)

For on-site engineers, correctly completing communication initialization is a prerequisite for stable system operation. Taking TSX SCG 1131 as an example, typical configuration steps are given below.

5.1 Construction of Configuration Table

Define an 8-character table (e.g. named 'COMVNet') and fill in the following in order:

Example value of word offset content (Modbus slave, 9600/8/N/1)

Function code 02 (Modbus/Jbus slave)

Data bit 08

2 parity check 00 (none)

3 Stop Position 01

4 baud rate 05 (9600 bps)

5 send back display 00 (disabled)

6 receive feedback 00 (disabled)

7 reserved/spare 00

Baud rate code reference: 03=4800, 05=9600, 06=19200.

5.2 Initialization program segment

Use text function blocks (such as TET1) to send the configuration table to the module. Usually executed once in the first scanning cycle of the PLC (through the contactor flag).

5.3 Sending and Receiving Data

Send data: Fill up to 30 bytes into the source table, call the TEXT block, and select "Send with timeout confirmation" as the request code.

Receive data: Call the TEXT block, specify the receive buffer address, and select "Receive with timeout" for the request code.

Suggest polling the status word in the loop to ensure communication is complete before proceeding to the next step. For multi frame long data, it is necessary to write a simple state machine to manage frame numbering and verification.

Common troubleshooting and maintenance

Based on years of on-site experience, TSX 17 communication related faults are mainly concentrated in the following categories. The following provides a systematic troubleshooting approach.

6.1 PLC unable to communicate with module

Phenomenon: Status word display module does not exist or communication timeout.

Possible reasons:

Module not correctly inserted into I/O slot or power not supplied

PL7-2 language card does not support this communication function

The configuration table was not sent correctly (or sent at the wrong time)

Troubleshooting steps:

Check the indicator lights on the module (if any). In most cases, the LED lights up after the module is powered on.

Confirm that the PL7-2 language card model installed in the CPU slot is consistent with the document requirements.

Forcefully ensure that the configuration block is executed only once at the beginning of the program, and use a timer to delay sending for several scanning cycles.

6.2 RS232 communication data error or garbled code

Phenomenon: Received characters but data error, or no response at all.

Possible reasons:

The baud rate, data bits, parity check do not match the other device

Cable wiring errors (most common problem)

Poor grounding leads to common mode interference

Troubleshooting steps:

Use serial monitoring tools (such as PC+serial assistant) to monitor the TX/RX lines of TSX 17 and confirm the actual waveform and bitrate.

Verify cable connection: The RS232 port of TSX SCG 1131 uses a standard DB9 male connector, with pin definitions of 2-TX, 3-RX, 5-GND. Cross connection (2-3, 3-2, 5-5) is required for communication with PC.

Check if the shielding layer is single ended grounded to avoid ground circulation.

6.3 UNI-TELWAY bus communication failure

Phenomenon: The master station cannot access the slave station, or the server is unresponsive.

Possible reasons:

Bus terminal resistance not set correctly

Duplicate station address

Cable breakage or non-standard tap changer (such as not using TSX SCA 62)

Troubleshooting steps:

Check if terminal resistors (usually 120 Ω) are configured at both ends of the bus.

Verify the addresses of all sites (configured through PL7-2) to ensure uniqueness.

Dismantle the site in sections and use resistance measurement method to check the bus continuity and short circuit situation.

Confirm that all T-connections are through TSX SCA 62 sockets and cannot be directly connected with three-way terminals.

6.4 Modbus communication timeout or abnormal response

Phenomenon: After the master station sends a request, the slave station does not respond or responds incorrectly.

Possible reasons:

Wrong setting of slave station address

Function code or register address not supported

Response exceeds timeout (e.g. slave scan cycle too long)

Troubleshooting steps:

Use Modbus scanning tools (such as ModScan) to independently test the slave station and determine whether the problem is caused by the slave station itself or the bus.

In the text block call of TSX 17 program, appropriately increase the timeout setting value (such as 500 ms).

Confirm whether the slave device supports the current requested function code (such as 03 read hold register, 06 write single register, etc.).

6.5 Intermittent communication interruption or data loss

Phenomenon: Most of the time it is normal, but occasionally data is lost or errors are reported.

Possible reasons:

Electrical interference (during the operation of frequency converters and contactors)

Power supply fluctuation

RS232 cable too long (over 15 meters)

Troubleshooting steps:

Check if the communication cable is laid separately from the power cable (minimum distance of 30cm).

Add a magnetic ring (ferrite) to the RS232 cable.

If the distance is indeed long, consider replacing it with an RS485 converter or fiber optic modem.

Add retry mechanism in PLC program: automatically resend up to 3 times when timeout or verification error is detected.

Replacement and upgrade strategy for discontinued modules

Considering that TSX SCG 1131, SCG 1161, and TSX 17 ACC5 have all been discontinued, the following are three feasible response plans, ranked by recommendation level.

7.1 Purchase high-quality second-hand/refurbished modules

Purchase tested inventory modules from professional second-hand automation equipment suppliers such as Artisan Technology Group, Radwell, etc. These modules typically come with a short-term warranty (30-90 days), which can help the equipment run for several more years.

Notes:

Confirm that the supplier has a functional testing process (such as verifying each port and protocol).

Require clear product images and batch numbers to avoid counterfeit products.

Try to purchase spare modules in the same batch.

7.2 Using Protocol Conversion Gateway to Implement Communication Upgrade

If the original system only needs to communicate with the upper layer monitoring (rather than interconnect with other old-fashioned UNI-TELWAY devices), it can be considered to connect the serial port of TSX 17 (or from the programming port of PLC when it cannot be obtained through a damaged dedicated module) to a modern protocol gateway.

Recommended product type:

RS232 ←→ Modbus TCP gateway: Brands such as Anybus, HMS, Moxa, etc. Using TSX 17 as a Modbus slave (via SCG 1131), the gateway converts Modbus RTU to Modbus TCP, and the upper computer accesses it through Ethernet.

RS232 ←→ Profinet/Ethernet/IP gateway: suitable for systems led by Siemens or Rockwell.

Advantages: No need to modify the hardware and programs on the TSX 17 side, only external devices need to be added.

Disadvantage: Increased cost and potential latency (usually<10 ms, acceptable).

7.3 Progressive PLC Replacement

For factories that are conditionally shut down for system upgrades, TSX 17 can be gradually phased out and replaced with modern modular PLCs (such as Modicon M241/M251, supporting Native Ethernet/IP and Modbus TCP). At the same time, it is necessary to:

Rewrite the control logic (migrate from PL7-2 to SoMachine or EcoStruxure Machine Expert).

Keep the original I/O modules (if compatible) or replace them together.

Unify the communication interface to Ethernet to completely solve the spare parts problem.

Suggestion: Replace non critical equipment pilot projects first, accumulate experience, and then promote to critical areas.

7.4 Self made signal conversion board (high difficulty, not recommended)

For extremely special situations where second-hand modules cannot be purchased, the TSX 17 terminal port or backplane bus signal can be analyzed to design a protocol converter based on a microcontroller. But the risk is extremely high and time-consuming, only suitable for teams with reverse engineering capabilities.

Suggestions for Engineering Maintenance and Spare Parts Management

To maximize the service life of the TSX 17 system, it is recommended to implement the following maintenance system:

Regular backup: Use PL7-2 software (running on a Windows 98/XP virtual machine) to regularly upload programs and save them as files (such as. PLG). Simultaneously record configuration table parameters and wiring diagrams.

Environmental control: Keep the temperature inside the electrical cabinet below 50 ° C and the humidity between 30% and 80% to avoid dust accumulation and poor module heat dissipation.

Static protection: When plugging and unplugging communication modules, operators should wear anti-static wristbands to avoid damaging sensitive CMOS circuits.

Spare parts inventory: Reserve at least one TSX SCG 1131 (or SCG 1161) and one TSX CSC 015 connecting cable. Purchase promptly when available in the second-hand market.

Regular inspection: Check all communication cable connections for looseness every six months, and use an oscilloscope to measure the RS232 voltage waveform (between -5V and -15V when idle).

Case Study: Repair of Serial Communication Interruption in a Packaging Line

Background: A heat shrink packaging machine controlled by TSX 17-20 frequently experiences an "upper computer data update failure" alarm. The packaging machine communicates with a weighing instrument (Modbus RTU slave) through TSX SCG 1131.

Troubleshooting process:

Check the PLC status word and find that the receive timeout flag is frequently set.

Using a serial port monitoring tool to connect the line, it was found that when a nearby large frequency converter accelerates, there is obvious glitch noise on the RS232 line.

Replace the communication cable from ordinary unshielded wire to twisted pair shielded wire, and ground the shielding layer on the PLC side.

At the same time, increase the timeout retry count from 1 to 3 in the PLC program.

Fault elimination.

Inspiration: The anti-interference design of old systems is often insufficient, and simple shielding and improved grounding can greatly enhance reliability.