Protocol ALPHA-MODBUS

Description

The ALPHA-MODBUS protocol is a binary, transparent serial protocol for communication with Mitsubishi ALPHA programmable logic controllers (PLCs). Between the Advantech router and the dispatching system, the MODBUS-TCP protocol is used. On the serial line between the router and the PLC, the proprietary α2 protocol is used. The router performs real-time, transparent conversion of data flowing in both directions.

Communication principle — Advantech Router with ALPHA-MODBUS

In Client mode, the router communicates with the PLC at a configured interval. If no interval is configured, data is not sent regularly. Alarm flags are also detected within the configurable interval. Data is sent to the server either periodically according to the configured interval, or immediately when an alarm is detected. After the router reads and forwards the required data, the alarm flag is reset to inactive.

In Server mode, the router communicates only upon request from the dispatching system, and also supports writing values into the Mitsubishi ALPHA PLC.

Configuration

Introduction

Caution

Multiple programs cannot share access to the same serial interface. If a serial interface (on an expansion port or a USB ↔ serial converter) is enabled in the ALPHA-MODBUS Router App, it must not be enabled in any other Router App or in the system.

The application configuration is accessible from the Customization section under the Router Apps menu item.

For version 1.6.1 or earlier, a separate instance of the Router App is created for each serial interface during installation (e.g., ALPHA-MODBUS 1 and ALPHA-MODBUS 2).

Newer versions install only a single instance of the Router App, which manages settings for all available interfaces. The application menu (shown in the figure below) displays only items corresponding to physically present hardware. For example, if the router does not have a second expansion port or a USB connector, those items will not be shown.

Newer versions also support the USB port, if available on the router, for connecting a serial converter.

Caution

If upgrading from version 1.6.1 or earlier to a newer version, the Expansion Port 2 interface must be manually reconfigured — the configuration is not transferred automatically.

ALPHA-MODBUS router app main menu (versions later than 1.6.1)

Configuration Items

For each interface, the items shown in the figure below can be configured.

Item	Description
Port Type	Indicates the detected type of the serial interface on the expansion port, or whether a USB ↔ serial converter is connected.
Baudrate	Communication speed in bits per second (bit/s).
Data Bits	Number of data bits: 7 or 8.
Parity	Parity setting: none, even, or odd.
Stop Bits	Number of stop bits: 1 or 2.
Server Address	IP address of the server (Client mode only).
TCP Port	TCP port number of the server or client.
Station Number	Address of the connected PLC.
Data Reading Period	Period for reading data (Client mode only).
Alarm Reading Period	Period for detecting alarms (Client mode only).
Starting Address	Starting address of the data area to send (Client mode only).
Number of Registers	Length of the data area to send (Client mode only).
Alarm Address	Address of the alarm register (Client mode only).

Interface configuration items

Map of MODBUS/ALPHA Device Registers

Notes:

More detailed information can be found in the Mitsubishi α2 Communication Manual and Mitsubishi α Software Manual.
All items are 16-bit; the higher byte (MSB) is sent first.

RefNum MODBUS	ALPHA Device	Can Write	Note
1	System Bit 1–16	NO
2	System Bit 17–24	NO	Bits 25–32 always 0
3	Input Terminal 1–15	YES	Bit 16 is always 0
4	Reserve	YES	Not used, always 0
5	External Input 1–4	YES	Bits 5–16 always 0
6	Output Terminal 1–9	YES	Bits 10–16 always 0
7	External Output 1–4	YES	Bits 5–16 always 0
8	Key Input 1–8	YES	Bits 9–16 always 0
9	Link Input 1–4	YES	Bits 5–16 always 0
10	Link Output 1–4	YES	Bits 5–16 always 0
11	Control Device 1–4	YES	Bits 5–16 always 0
12–16	Reserve	NO	Not used, always 0
17	Analog In 1	NO
18	Analog In 2	NO
19	Analog In 3	NO
20	Analog In 4	NO
21	Analog In 5	NO
22	Analog In 6	NO
23	Analog In 7	NO
24	Analog In 8	NO
25–256	Reserve	NO	Not used, always 0
257	System Bit 1–16	NO
258	System Bit 17–24	NO	Bits 25–32 always 0
259	Input Terminal 1–8	YES	Bits 9–16 always 0
260	Reserve	YES	Not used, always 0
261	External Input 1–4	YES	Bits 5–16 always 0
262	Output Terminal 1–6	YES	Bits 7–16 always 0
263	External Output 1–4	YES	Bits 5–16 always 0
264	Key Input 1–8	YES	Bits 9–16 always 0
265	Link Input 1–4	YES	Bits 5–16 always 0
266	Link Output 1–4	YES	Bits 5–16 always 0
267	Control Device 1–4	YES	Bits 5–16 always 0
268–512	Reserve	NO	Not used, always 0
513	Communication Bit Device 1	YES
514	Communication Bit Device 2	YES
515	Communication Bit Device 3	YES
516–612	Communication Bit Device 4 – Communication Bit Device 100	YES
613–1024	Reserve	NO	Not used, always 0
1025	Communication Word Device 1	YES
1026	Communication Word Device 2	YES
1027	Communication Word Device 3	YES
1028–1124	Communication Word Device 4 – Communication Word Device 100	YES
1125–1536	Reserve	NO	Not used, always 0
1537	RTC — Year	YES
1538	RTC — Month	YES
1539	RTC — Day	YES
1540	RTC — Hour	YES
1541	RTC — Min	YES
1542	RTC — Sec	YES
1543	RTC — Adj	YES
1544	RTC — DoW	NO
1545	RTC — Status	NO
1546–2048	Reserve	NO	Not used, always 0
2049	Run/Stop	YES	Write only — cannot be read. 1 = Run, 0 = Stop
2050–8192	Reserve	NO	Not used, always 0
8193–8216	System Bit 1 – System Bit 24	NO
8217–8448	Reserve	NO	Not used, always 0
8449–8463	Input Terminal 1 – Input Terminal 15	YES
8464–8704	Reserve	NO	Not used, always 0
8705–8708	External Input 1 – External Input 4	YES
8709–8960	Reserve	NO	Not used, always 0
8961–8969	Output Terminal 1 – Output Terminal 9	YES
8970–9216	Reserve	NO	Not used, always 0
9217–9220	External Output 1 – External Output 4	YES
9221–9472	Reserve	NO	Not used, always 0
9473–9480	Key Input 1 – Key Input 8	YES
9481–9728	Reserve	NO	Not used, always 0
9279–9282	Link Input 1 – Link Input 4	YES
9283–9984	Reserve	NO	Not used, always 0
9985–9988	Link Output 1 – Link Output 4	YES
9989–10240	Reserve	NO	Not used, always 0
10241–10244	Control Device 1 – Control Device 4	YES

Map of MODBUS/ALPHA device registers