MITSUBISHI ELECTRIC GOT1000 Modbus Connection

MITSUBISHI ELECTRIC GOT1000 Series Connection Configuration and Troubleshooting Complete Guide

The Mitsubishi GOT1000 series graphic operation terminal, with its powerful communication capabilities, not only supports multiple connection methods with Mitsubishi PLC, but also exchanges data with non Mitsubishi devices, third-party controllers, and various peripheral devices (barcode readers, RFID, printers, etc.) through MODBUS/RTU, MODBUS/TCP, and microcomputer specific protocols. However, in practical engineering, engineers often encounter issues such as mismatched communication parameters, incorrect cable wiring, and improper protocol format selection, leading to monitoring failures or data confusion. This article is based on the GOT1000 series connection manual (microcomputer, MODBUS products, peripheral devices section), and systematically outlines the entire process from hardware wiring, communication interface configuration to message format selection and fault code troubleshooting. Whether you are connecting a GOT to a MODBUS device for the first time or debugging an unstable RS-485 link, this article will provide operational guidance that can be directly used on site.

GOT1000 series communication interface and preparatory settings

2.1 Communication interface types and physical connections

The GOT1000 series provides multiple physical interfaces:

RS-232: 9-pin D-sub (male or female), with a maximum transmission distance of 15 meters, suitable for point-to-point connections.

RS-422/485: 9-pin D-sub or 14 pin/20 pin dedicated connector (depending on model), maximum transmission distance of 1200 meters (RS-422/485), supports multi-point connection (up to 31 slaves).

Ethernet: RJ45, 10/100Mbps, using direct or crossover Ethernet cables, can connect multiple devices through a hub.

Important wiring specifications:

The length of the RS-232 cable should not exceed 15 meters (as explicitly warned in the manual). Excessive length can lead to signal attenuation and errors.

RS-422/485 must use twisted pair shielded cables and correctly connect terminal resistors. The GOT side usually sets the terminal resistance (110 Ω or 330 Ω) through a dip switch or internal jumper. The terminal device must be in the "termination" position, and the intermediate device must be "disabled".

When connecting to Ethernet, the IP address must not end in 0 or 255 (for example, 192.168.0.0 or 192.168.0.255 are reserved by the system), and when multiple GOTs are connected to the same network, the use of the IP address 192.168.0.18 is prohibited, otherwise it will cause address conflicts and communication abnormalities.

2.2 Communication driver and channel configuration

In GT Designer 3 software, the following two key settings need to be made:

2.2.1 Controller Setting

Select menu [Common] → [Controller Setting].

Select the channel number to be used (CH1-CH4 for connecting controllers, CH8 for barcode readers/RFID/fingerprint authentication and other peripherals that require GOT power supply).

Settings: Manufacturer, Controller Type, I/F, Driver.

For MODBUS/RTU devices: Manufacturer=MODBUS, Controller Type=MODBUS, Driver=MODBUS/RTU.

For microcomputers (custom hosts): Manufacturer=Others, Controller Type=Computer, Driver=Computer (serial) or Ethernet (MICROCOMPUTER).

Click on 'Detail setting' to enter the detailed communication parameter configuration.

2.2.2 I/F Communication Setting

In [Common] → [I/F Communication Setting], assign a channel number (CH No.) to each physical interface (standard I/F-1, I/F-2, etc.).

Channel number 0 indicates not in use; Channel numbers 1-4 are used for communication with the controller; Channel number 8 is specifically designed for peripherals that require GOT to provide 5V/24V power (barcode readers, RFID, etc.).

Important: The same channel number cannot be used for multiple functions simultaneously. For example, if CH8 is already used for fingerprint authentication, it cannot be connected to a barcode reader at the same time.

Microcomputer connection (serial and Ethernet)

The microcomputer (or "host") connection function allows external PCs, microcontrollers, or PLCs to read and write data through the internal virtual device area (D, R, L, M, SD, SM, etc.) of GOT, and supports interrupt output.

3.1 Serial Connection (RS-232/RS-422)

System configuration:

Point to point connection: The GOT is directly connected to the host via RS-232 or RS-422 cable.

Multi point connection: Up to 4 GOTs can be cascaded to one host via RS-232/RS-422 (using dedicated connection cables and connectors).

Message format: GOT supports 15 different formats, including formats compatible with old models GOT-A900/F900, A-series 1C frames, QnA compatible 3C/4C frames, and Digital Electronics Corporation's memory linking method. Common formats include:

Format 1/2 (GOT-A900 series microcomputer connection): Simple ASCII format, no station number.

Format 7-10 (QnA compatible with 3C/4C frames): Supports multiple station numbers and sub station numbers, suitable for complex networks.

Format 14/15 (GOT-F900 series microcomputer connection): Supports batch read/write and fill commands.

Key points of host side programming:

The command format includes: STX (02h), commands (such as RD, WD), device address (4-digit ASCII hexadecimal), data length, ETX (03h), and checksum.

Interrupt output: When the status of the internal devices (SM0~SM49) in GOT changes or special events (such as screen switching or numerical input completion) occur, GOT will automatically send 1/2/4 byte interrupt data to the host. Enable 'Interrupt Data Byte' and 'Special Interrupt Code' in the detailed communication settings.

3.2 Ethernet Connection

Supported protocols: UDP/IP or TCP/IP. Interrupt output is only valid under TCP/IP.

Set project:

GOT IP address, subnet mask, default gateway.

Ethernet download port number (default 5014) and GOT communication port number (default 5021).

32-bit storage order: LH Order (low word first) or HL Order (high word first).

Notes:

When multiple controllers send commands simultaneously under UDP/IP, GOT may not be able to receive all of them and needs to retry.

When connecting multiple GOTs, each GOT must have a different PLC No. (station number) set and ensure that the IP address is not duplicated.

3.3 Troubleshooting: Common errors in microcomputer connection

Possible causes and solutions for the phenomenon

GOT is unresponsive, POWER LED is normal. The serial cable is too long (>15m) or the wiring is incorrect. Shorten the cable to within 15 meters. Check the RS-232 pin definition (TX/RX cross, SG direct connection)

Read all data as 0 or garbled baud rate/data bits/stop bits/check for inconsistency. Verify that the detailed settings for GOT communication are exactly the same as those on the host side; Confirm the actual signal using an oscilloscope or serial monitoring tool

Error code SD2=1 or 101 (parity error). If the parity settings do not match, change the parity of both parties to the same (None/Even/Odd); Check cable shielding and grounding

Error code SD2=4 or 104 (communication message error): The correct frame termination symbol (ETX or CR) has not been received. Confirm that the message sent by the host ends with ETX (03h) and/or CR+LF; Check if the upper limit of the receiving buffer has been exceeded

Interrupt output has no response and interrupt data byte is not enabled or SM52 is set to ON. Set interrupt data byte ≥ 1 in the communication detailed settings and confirm that SM52=OFF (interrupt output allowed); Replace UDP with TCP/IP

Ethernet connection timeout (Ping not working), IP address conflict or network cable failure, perform Ping test; Check if the GOT IP address ends in. 0 or. 255; Ensure that the switch supports 100BASE-TX

MODBUS/RTU connection

As a MODBUS master station, GOT can connect up to 31 MODBUS/RTU slave station devices (such as frequency converters, instruments, PLCs).

4.1 Wiring points

RS-232: point-to-point, maximum 15 meters.

RS-422/485: multi-point, maximum 1200 meters. Twisted shielded wires must be used. Terminal resistance: When the GOT is located at the end of the bus, set the terminal resistance to 110 Ω (1 pair of wires) or 330 Ω (2 pairs of wires). Intermediate nodes must disable terminal resistors.

Supports 2-wire (half duplex) and 4-wire (full duplex) connections. In the 2-wire system, SDA and RDA need to be short circuited, and SDB and RDB need to be short circuited.

4.2 GOT Side Settings

Communication speed: 9600/19200/38400/57600/115200 bps.

Data bits: 8-bit (MODBUS standard), stop bit 1 or 2, parity check none/odd/even.

Host address: GOT's station number (1-247). Note: The slave station must contain the same device as this station number (for reading).

Number of retries: default 3 times.

Delay time: Some MODBUS devices require frame intervals greater than 3.5 characters, and the delay can be increased here (0-300ms).

4.3 Supported MODBUS Function Codes

Function code name, maximum number of points per use

01 Reading Coil 2000

02 Read Discrete Input 2000

03 Read and hold register 125

04 Read input register 125

05 Writing a single coil 1

06 Write a single register 1

0F writes multiple coils 1968

10 write multiple registers 123

14 Read File Record 124

15 Writing Document Records 122

4.4 Common faults and troubleshooting

Possible causes and solutions for error phenomena

GOT alarm "system alarm (402): timeout error" slave station not responding or address error check slave station power and station number; Confirm that the communication parameters are consistent; Check the terminal resistance

Partial data reading is correct, and some incorrect function codes are not supported by the slave station. Disable unsupported function codes (such as 0F, 10) in GS570~GS576; Or use simpler function codes (01/03)

The write operation is invalid. When broadcasting write, the slave station does not support broadcasting broadcast address (0), which is only applicable for writing; To read, a specific station number must be specified

Intermittent RS-485 bus reflection or interference during communication ensures that only the terminal resistors at both ends are connected; Use shielded twisted pair cables and single ended grounding; Reduce communication speed

4.5 MODBUS Communication Control Function (GS Equipment)

When the function code of the connected MODBUS device is limited or the length of a single frame of data is small, it can be dynamically adjusted through the special registers (GS570~GS576) inside GOT:

GS570.0: Set to 1 to disable function code 0F (write multiple coils); GS570.1: Set to 1 to disable function code 10 (write multiple registers).

GS571~GS576: Set the maximum number of points allowed for each function code separately (for example, the maximum number of reading coils can be set to 1000 instead of 2000).

GS579: Used for selecting shared or independent settings when multiple channels are available (one set of GS590~GS617 per channel).

Important: These GS registers must be set at once through project scripts during GOT startup, and any changes made during runtime may cause communication errors.

MODBUS/TCP connection

GOT, as a MODBUS/TCP client, can connect to multiple server devices (such as Schneider Modicon, Yokogawa STARDOM, etc.).

5.1 Key points of setting

In the controller settings, select "MODBUS/TCP, Gateway" for the Driver.

Set the network number (1-239), PLC number (station number, 1-247), and IP address of GOT.

In the "Ethernet Settings" tab, add the IP address and port number (usually 502) of the target MODBUS/TCP server, as well as the network and station numbers of the server.

5.2 IP address restrictions when connecting multiple GOTs

When there is only one GOT in the network, other controllers are prohibited from using the IP address 192.168.0.18.

When there are multiple GOTs, no device (including GOTs) should use 192.168.0.18, otherwise it will cause address duplication and communication failure.

5.3 Troubleshooting

Possible causes and actions of the phenomenon

Connection failed, GOT shows' Target IP unresponsive '. The server port is not 502 or the firewall is blocking the confirmation server from listening on the port and allowing it in the router

Data read error, register address mapping error check, device address translation (Modbus address starts from 0, GOT device number starts from 1, pay attention to offset)

Periodic timeout: excessive network load using a switch hub; Increase the timeout period (up to 90 seconds); Reduce the number of monitoring points

Key points for connecting peripheral devices (barcode/printer/RFID/external I/O)

6.1 Barcode Reader Connection

Channel number 8 (standard interface) must be used and GOT needs to provide power. If the barcode reader is self powered, it can be connected to channels 5-7.

The termination symbol must be set (such as CR, LF) and consistent with the output of the barcode reader.

Specify the storage device for receiving data (such as D0 offset) through the "Bar Code" peripheral settings.

Common problem: Incomplete scanning data → Check the byte order (Low/High) and padding characters (Space/null) for writing.

6.2 Printer Connection

Supports PictBridge compatible printers (via USB) and serial printers (RS-232).

The serial printer must have the same baud rate, data bits, etc. as the GOT settings. Note: The hard copy function requires data bits of 8 bits.

Problem: The printer sends a "ready" signal too early during initialization, causing errors when GOT starts printing. Before restarting the printer, disconnect the USB cable and wait for complete initialization before connecting again.

6.3 RFID Connection

Supports multiple specialized protocols (such as LSIS, MARS TOHKEN ICU series, etc.), selected through "Format".

The external authentication function must use channel 8. If RFID requires GOT power supply, it can only use channel 8.

Multi reader interlock: Interlocking needs to be implemented in the controller program to prevent simultaneous communication.

6.4 External I/O devices (operation panel)

Use GT15-DIO (positive common input/drain type output) or GT15-DIOR (negative common input/source type output).

Supports 16 point input/16 point output, or 128 point matrix input (through scanning signals).

When wiring, attention should be paid to the direction of the diode (each switch must be connected in series with a diode to prevent crosstalk when inputting the matrix).

System level fault diagnosis method

7.1 Use GOT's built-in communication monitoring function

Enter the Utility menu of GOT ->"Communication Settings" ->"Comm. Monitor" to view the communication status, send/receive frame count, and latest errors of each channel.

For Ethernet connections, you can perform a Ping test through the Windows command prompt or perform a "PING test" in GT Designer 3.

7.2 Interpretation of Error Codes in Special Data Register (SD2)

When a communication error occurs, GOT will store the error code in the internal SD2 register. Common values:

Error code (decimal) meaning handling

1 (101) Parity Error Check Check Check Bit Setting and Cable Quality

2 (102) frame error check stop bit and data bit

3 (103) Exceeding limit error reduces baud rate or checks CPU load

4 (104) Message error check message format and terminator

5 Command Error Confirmation: Is the function code used supported

105 timeout error check for slave power, cable, and station number

6 (107) Clock data setting error check if the date/week written is correct

7.3 Use GS equipment for advanced control

GS570~GS576: Adjust the support range of MODBUS function codes to solve specific device compatibility issues.

GS579: Separate or share communication settings for multiple channels.

GS580~GS583 (microcomputer connection extension settings): Enable "digital compatibility signal" to achieve full compatibility with the memory linking method of Digital Electronics Corporation.

7.4 Quick troubleshooting process for hardware failures

Check the power supply: The GOT and all connected devices are powered on normally without overload (the calculated total current does not exceed the GOT power supply capacity).

Check cables: Use a multimeter to test the continuity of all wires and confirm that the shielding layer is grounded at one end.

Isolation test: Disconnect all slave stations, connect only one known good slave station, and gradually add other devices.

Use loopback test: Short circuit the TXD and RXD of RS-232, send data and observe whether they can echo, and verify whether the hardware of the GOT port is normal.

View GOT system alarm: Touch the upper right corner of the screen or call the system alarm window to obtain the specific alarm number (such as 402=timeout, 403=communication error).

Maintenance and preventive measures

Regularly check communication parameters: export project settings in GT Designer 3 and compare them with actual parameters on site.

Backup project: Use SD card or CF card to backup GOT project data and OS.

Firmware update: Regularly visit the Mitsubishi official website to upgrade the standard monitoring OS, communication drivers, and extended function OS.

Environmental protection: Avoid exposing GOT to oil mist, chemicals, or extreme temperatures, and use protective covers if necessary.

Grounding: Ensure that the FG terminal of GOT is reliably connected to the protective ground of the cabinet, and the grounding resistance is ≤ 100 Ω.