Complete Guide to Field Application and Troubleshooting of Mitsubishi GT15-RS2/4 Serial Communication Unit

Align insertion: Align the expansion interface of the serial communication unit with the expansion connector of the GOT, and push it in parallel until it feels fully engaged.

Tighten screws: Use a Phillips screwdriver to tighten the two mounting screws on the unit. The torque range is 0.36~0.48 N · m. Being too tight can damage the plastic studs, while being too loose can lead to poor contact.

Multi level expansion: If additional expansion units (such as Ethernet or bus connections) need to be installed after the already installed serial unit, the connector cover and sticker on the front end of the unit need to be removed. If the expansion is not continued, the attached anti-static sticker should be pasted to cover the top of the screw, and the connector cover should be kept to prevent foreign objects from entering.

Warning: When disassembling the serial communication unit, it is necessary to hold the "PULL" indicator on the side of the unit and pull it out horizontally. Do not tilt or shake it, otherwise the internal connector pins will be damaged.

3.2 Terminal Block Installation (GT15-RS4-TE only)

The terminal block of GT15-RS4-TE is pluggable. It is recommended to unplug the terminal block from the unit before wiring:

Align the protrusion of the terminal block socket with the guide groove on the unit and insert it vertically.

Tighten the fixing screws on both sides of the terminal block (torque 0.20~0.25 N · m) to prevent vibration loosening.

Practical tip: In a multi expansion layer structure, there is no need to remove all expansion units from the GOT. Simply remove the terminal block of the target GT15-RS4-TE for wiring or replacement, greatly reducing downtime.

Chapter 4 Wiring Specification and Terminal Resistance Configuration

Good wiring is the cornerstone of stable serial communication. The following wiring instructions are provided for three different models.

4.1 GT15-RS2-9P (RS-232) Wiring Points

Connector: D-sub 9-pin male connector, compatible with standard straight or crossover cables (depending on the definition of the end device).

Maximum distance: 15 meters, it is recommended to use shielded RS-232 dedicated cables (such as Mitsubishi GT01-C □□□□ -9P series).

Foot position definition (reference standard RS-232 DTE):

2-pin: RXD (receive data)

3-pin: TXD (sending data)

5 feet: SG (signal ground)

Other pins (such as 4, 6, 7, 8) can be disconnected in simple three wire communication.

Shielding treatment: The shielding layer is only grounded on the single end of the GOT side to avoid ground circulation.

Common faults: Sometimes there is no communication and accompanied by garbled code → Check if the transmission and reception are cross connected (the TXD of GOT should be connected to the RXD of the device). If the peer device is DCE (such as a modem), a direct line is required.

4.2 GT15-RS4-9S (RS-422/485 D-sub) wiring

Connector: D-sub 9-pin female connector. Recommend using Mitsubishi specific cables (such as GT01-C □ R4-25P).

Signal allocation (typical RS-422/485 4-wire system):

RDA (receive A+), RDB (receive B -)

SDA (send A+), SDB (send B -)

SG (Signal Ground)

ERA, ERB (optional RS-422 full duplex control, generally not connected)

Two wire half duplex: RDA and SDA need to be short circuited, RDB and SDB need to be short circuited (there is no automatic switching inside the unit).

Terminal resistor: Control the built-in 100 Ω resistor through DIP switch (positions 1 and 2 of SW1). Only devices located at the physical end of communication lines need to have terminal resistors connected.

4.3 GT15-RS4-TE (terminal block type) wiring

This is the most flexible model on site and also a high-risk area for malfunctions. The correct wiring steps are as follows:

4.3.1 Wire preparation

Peel off the cable sheath by 7mm (0.28 inches) to expose the copper core.

If using multiple strands of flexible wire, it is recommended to crimp U-shaped or tubular cold pressed terminals to avoid loose wire short circuits.

4.3.2 Shielding layer connection (key!)

The attachment provides a "plate type solerless terminal" for fixing the shielding braided mesh:

Fold the shielding braided mesh of RS-422/485 cable backwards to expose a section of approximately 10mm.

Press the shielding net under the board terminal and tighten it with wire clamps.

Connect the board terminal to the ground terminal (marked as FG or SLD) on the terminal block.

Attention: The shielding layer cannot be directly screwed onto the terminal screw, otherwise it is easy to loosen.

4.3.3 Wire Connection

Connect the wires according to the markings on the terminal block (such as RDA, RDB, SDA, SDB, SG).

Tighten the wire screw to a torque of 0.5~0.6 N · m. Too small can easily loosen, and too large pressure can break the wire core.

The insertion direction must be horizontal (parallel to the long side of the terminal block). If inserted vertically, it is prone to detachment after vibration.

4.3.4 Terminal Resistance Setting (DIP Switch)

The DIP switch of GT15-RS4-TE is located on the side of the unit (SW1, two position switch):

Built in terminal resistor ON: Turn both SW1-1 and SW1-2 to the ON position (connect 100 Ω).