MODBUS

MODBUS

Modicon Communication Bus (MODBUS) is an application layer protocol that facilitates client-server communication between a switch (server) and a device running MODBUS client software (client). It operates effectively over a serial line, allowing you to connect a computer to a remote terminal unit (RTU) in supervisory control and data acquisition (SCADA) systems.

MODBUS over Ethernet TCP/IP

MODBUS also functions on Ethernet TCP/IP networks. Use MODBUS TCP over an Ethernet network to connect the switch to devices such as intelligent electronic devices (IEDs), distributed controllers, and substation routers. It is also used to connect IP phones, wireless access points, and other network devices including redundant substation switches.

Role of clients and servers

The client in this setup can be an IED or a human-machine interface (HMI) application that remotely configures and manages devices running MODBUS TCP. In this scenario, the switch serves as the server.

Message communication using MODBUS TCP

The switch encapsulates a request or response message within a MODBUS TCP application data unit (ADU). Clients communicate by sending messages to TCP ports on switches.

Cisco Catalyst IE3x00 Modbus TCP Registers

This document lists the read-only registers for IE3x00 models. MODBUS clients use them to communicate with a MODBUS server (the switch). There are no writable registers.

Table 1. System Info Registers
Address # of registers Description R/W Format
800 64 Product ID R Text
840 64 Software Image Name R Text
880 64 Software Image Version R Text
8C0 64 Host Name R Text
900 64 Alarm 1 – Description R Text
940 64 Alarm 2 – Description R Text
980 1 Alarm 1 – Status R Uint16
981 1 Alarm 2 – Status R Uint16
982 1 Number of 10/100 Ethernet Ports R Uint16
983 1 Number of Gig Ethernet Ports R Uint16
984 1 Number of Alarms R Uint16
985 1 Number of Power Supplies R Uint16
986 1 PS1 – Status R Uint16
987 1 PS2 – Status R Uint16
988 1 System Temperature (in Celsius) R Uint16
Table 2. 10 Port Registers
Address # of registers Description R/W Format
1000 64 Port 1 Name R Text
1040 64 Port 2 Name R Text
1080 64 Port 3 Name R Text
10C0 64 Port 4 Name R Text
1100 64 Port 5 Name R Text
1140 64 Port 6 Name R Text
1180 64 Port 7 Name R Text
11C0 64 Port 8 Name R Text
1200 64 Port 9 Name R Text
1240 64 Port 10 Name R Text
1280 1 Port 1 State R Uint16
1281 1 Port 2 State R Uint16
1282 1 Port 3 State R Uint16
1283 1 Port 4 State R Uint16
1284 1 Port 5 State R Uint16
1285 1 Port 6 State R Uint16
1286 1 Port 7 State R Uint16
1287 1 Port 8 State R Uint16
1288 1 Port 9 State R Uint16
1289 1 Port 10 State R Uint16
128A 4 Port 1 Statistics – Number of packets received R Uint64
128E 4 Port 2 Statistics – Number of packets received R Uint64
1292 4 Port 3 Statistics – Number of packets received R Uint64
1296 4 Port 4 Statistics – Number of packets received R Uint64
129A 4 Port 5 Statistics – Number of packets received R Uint64
129E 4 Port 6 Statistics – Number of packets received R Uint64
12A2 4 Port 7 Statistics – Number of packets received R Uint64
12A6 4 Port 8 Statistics – Number of packets received R Uint64
12AA 4 Port 9 Statistics – Number of packets received R Uint64
12AE 4 Port 10 Statistics – Number of packets received R Uint64
12B2 4 Port 1 Statistics – Number of packets sent R Uint64
12B6 4 Port 2 Statistics – Number of packets sent R Uint64
12BA 4 Port 3 Statistics – Number of packets sent R Uint64
12BE 4 Port 4 Statistics – Number of packets sent R Uint64
12C2 4 Port 5 Statistics – Number of packets sent R Uint64
12C6 4 Port 6 Statistics – Number of packets sent R Uint64
12CA 4 Port 7 Statistics – Number of packets sent R Uint64
12CE 4 Port 8 Statistics – Number of packets sent R Uint64
12D2 4 Port 9 Statistics – Number of packets sent R Uint64
12D6 4 Port 10 Statistics – Number of packets sent R Uint64
12DA 4 Port 1 Statistics – Number of bytes received R Uint64
12DE 4 Port 2 Statistics – Number of bytes received R Uint64
12E2 4 Port 3 Statistics – Number of bytes received R Uint64
12E6 4 Port 4 Statistics – Number of bytes received R Uint64
12EA 4 Port 5 Statistics – Number of bytes received R Uint64
12EE 4 Port 6 Statistics – Number of bytes received R Uint64
12F2 4 Port 7 Statistics – Number of bytes received R Uint64
12F6 4 Port 8 Statistics – Number of bytes received R Uint64
12FA 4 Port 9 Statistics – Number of bytes received R Uint64
12FE 4 Port 10 Statistics – Number of bytes received R Uint64
1302 4 Port 1 Statistics – Number of bytes sent R Uint64
1306 4 Port 2 Statistics – Number of bytes sent R Uint64
130A 4 Port 3 Statistics – Number of bytes sent R Uint64
130E 4 Port 4 Statistics – Number of bytes sent R Uint64
1312 4 Port 5 Statistics – Number of bytes sent R Uint64
1316 4 Port 6 Statistics – Number of bytes sent R Uint64
131A 4 Port 7 Statistics – Number of bytes sent R Uint64
131E 4 Port 8 Statistics – Number of bytes sent R Uint64
1322 4 Port 9 Statistics – Number of bytes sent R Uint64
1326 4 Port 10 Statistics – Number of bytes sent R Uint64
Table 3. 18 Port Registers
Address # of registers Description R/W Format
1000 64 Port 1 Name R Text
1040 64 Port 2 Name R Text
1080 64 Port 3 Name R Text
10C0 64 Port 4 Name R Text
1100 64 Port 5 Name R Text
1140 64 Port 6 Name R Text
1180 64 Port 7 Name R Text
11C0 64 Port 8 Name R Text
1200 64 Port 9 Name R Text
1240 64 Port 10 Name R Text
1280 64 Port 11 Name R Text
12C0 64 Port 12 Name R Text
1300 64 Port 13 Name R Text
1340 64 Port 14 Name R Text
1380 64 Port 15 Name R Text
13C0 64 Port 16 Name R Text
1400 64 Port 17 Name R Text
1440 64 Port 18 Name R Text
1480 1 Port 1 State R Uint16
1481 1 Port 2 State R Uint16
1482 1 Port 3 State R Uint16
1483 1 Port 4 State R Uint16
1484 1 Port 5 State R Uint16
1485 1 Port 6 State R Uint16
1486 1 Port 7 State R Uint16
1487 1 Port 8 State R Uint16
1488 1 Port 9 State R Uint16
1489 1 Port 10 State R Uint16
148A 1 Port 11 State R Uint16
148B 1 Port 12 State R Uint16
148C 1 Port 13 State R Uint16
148D 1 Port 14 State R Uint16
148E 1 Port 15 State R Uint16
148F 1 Port 16 State R Uint16
1490 1 Port 17 State R Uint16
1491 1 Port 18 State R Uint16
1492 4 Port 1 Statistics – Number of packets received R Uint64
1496 4 Port 2 Statistics – Number of packets received R Uint64
149A 4 Port 3 Statistics – Number of packets received R Uint64
149E 4 Port 4 Statistics – Number of packets received R Uint64
14A2 4 Port 5 Statistics – Number of packets received R Uint64
14A6 4 Port 6 Statistics – Number of packets received R Uint64
14AA 4 Port 7 Statistics – Number of packets received R Uint64
14AE 4 Port 8 Statistics – Number of packets received R Uint64
14B2 4 Port 9 Statistics – Number of packets received R Uint64
14B6 4 Port 10 Statistics – Number of packets received R Uint64
14BA 4 Port 11 Statistics – Number of packets received R Uint64
14BE 4 Port 12 Statistics – Number of packets received R Uint64
14C2 4 Port 13 Statistics – Number of packets received R Uint64
14C6 4 Port 14 Statistics – Number of packets received R Uint64
14CA 4 Port 15 Statistics – Number of packets received R Uint64
14CE 4 Port 16 Statistics – Number of packets received R Uint64
14D2 4 Port 17 Statistics – Number of packets received R Uint64
14D6 4 Port 18 Statistics – Number of packets received R Uint64
14DA 4 Port 1 Statistics – Number of packets sent R Uint64
14DE 4 Port 2 Statistics – Number of packets sent R Uint64
14E2 4 Port 3 Statistics – Number of packets sent R Uint64
14E6 4 Port 4 Statistics – Number of packets sent R Uint64
14EA 4 Port 5 Statistics – Number of packets sent R Uint64
14EE 4 Port 6 Statistics – Number of packets sent R Uint64
14F2 4 Port 7 Statistics – Number of packets sent R Uint64
14F6 4 Port 8 Statistics – Number of packets sent R Uint64
14FA 4 Port 9 Statistics – Number of packets sent R Uint64
14FE 4 Port 10 Statistics – Number of packets sent R Uint64
1502 4 Port 11 Statistics – Number of packets sent R Uint64
1506 4 Port 12 Statistics – Number of packets sent R Uint64
150A 4 Port 13 Statistics – Number of packets sent R Uint64
150E 4 Port 14 Statistics – Number of packets sent R Uint64
1512 4 Port 15 Statistics – Number of packets sent R Uint64
1516 4 Port 16 Statistics – Number of packets sent R Uint64
151A 4 Port 17 Statistics – Number of packets sent R Uint64
151E 4 Port 18 Statistics – Number of packets sent R Uint64
1522 4 Port 1 Statistics – Number of bytes received R Uint64
1526 4 Port 2 Statistics – Number of bytes received R Uint64
152A 4 Port 3 Statistics – Number of bytes received R Uint64
152E 4 Port 4 Statistics – Number of bytes received R Uint64
1532 4 Port 5 Statistics – Number of bytes received R Uint64
1536 4 Port 6 Statistics – Number of bytes received R Uint64
153A 4 Port 7 Statistics – Number of bytes received R Uint64
153E 4 Port 8 Statistics – Number of bytes received R Uint64
1542 4 Port 9 Statistics – Number of bytes received R Uint64
1546 4 Port 10 Statistics – Number of bytes received R Uint64
154A 4 Port 11 Statistics – Number of bytes received R Uint64
154E 4 Port 12 Statistics – Number of bytes received R Uint64
1552 4 Port 13 Statistics – Number of bytes received R Uint64
1556 4 Port 14 Statistics – Number of bytes received R Uint64
155A 4 Port 15 Statistics – Number of bytes received R Uint64
155E 4 Port 16 Statistics – Number of bytes received R Uint64
1562 4 Port 17 Statistics – Number of bytes received R Uint64
1566 4 Port 18 Statistics – Number of bytes received R Uint64
156A 4 Port 1 Statistics – Number of bytes sent R Uint64
156E 4 Port 2 Statistics – Number of bytes sent R Uint64
1572 4 Port 3 Statistics – Number of bytes sent R Uint64
1576 4 Port 4 Statistics – Number of bytes sent R Uint64
157A 4 Port 5 Statistics – Number of bytes sent R Uint64
157E 4 Port 6 Statistics – Number of bytes sent R Uint64
1582 4 Port 7 Statistics – Number of bytes sent R Uint64
1586 4 Port 8 Statistics – Number of bytes sent R Uint64
158A 4 Port 9 Statistics – Number of bytes sent R Uint64
158E 4 Port 10 Statistics – Number of bytes sent R Uint64
1592 4 Port 11 Statistics – Number of bytes sent R Uint64
1596 4 Port 12 Statistics – Number of bytes sent R Uint64
159A 4 Port 13 Statistics – Number of bytes sent R Uint64
159E 4 Port 14 Statistics – Number of bytes sent R Uint64
15A2 4 Port 15 Statistics – Number of bytes sent R Uint64
15A6 4 Port 16 Statistics – Number of bytes sent R Uint64
15AA 4 Port 17 Statistics – Number of bytes sent R Uint64
15AE 4 Port 18 Statistics – Number of bytes sent R Uint64
Table 4. 26 Port Registers
Address # of registers Description R/W Format
1000 64 Port 1 Name R Text
1040 64 Port 2 Name R Text
1080 64 Port 3 Name R Text
10C0 64 Port 4 Name R Text
1100 64 Port 5 Name R Text
1140 64 Port 6 Name R Text
1180 64 Port 7 Name R Text
11C0 64 Port 8 Name R Text
1200 64 Port 9 Name R Text
1240 64 Port 10 Name R Text
1280 64 Port 11 Name R Text
12C0 64 Port 12 Name R Text
1300 64 Port 13 Name R Text
1340 64 Port 14 Name R Text
1380 64 Port 15 Name R Text
13C0 64 Port 16 Name R Text
1400 64 Port 17 Name R Text
1440 64 Port 18 Name R Text
1480 64 Port 19 Name R Text
14C0 64 Port 20 Name R Text
1500 64 Port 21 Name R Text
1540 64 Port 22 Name R Text
1580 64 Port 23 Name R Text
15C0 64 Port 24 Name R Text
1600 64 Port 25 Name R Text
1640 64 Port 26 Name R Text
1680 1 Port 1 State R Uint16
1681 1 Port 2 State R Uint16
1682 1 Port 3 State R Uint16
1683 1 Port 4 State R Uint16
1684 1 Port 5 State R Uint16
1685 1 Port 6 State R Uint16
1686 1 Port 7 State R Uint16
1687 1 Port 8 State R Uint16
1688 1 Port 9 State R Uint16
1689 1 Port 10 State R Uint16
168A 1 Port 11 State R Uint16
168B 1 Port 12 State R Uint16
168C 1 Port 13 State R Uint16
168D 1 Port 14 State R Uint16
168E 1 Port 15 State R Uint16
168F 1 Port 16 State R Uint16
1690 1 Port 17 State R Uint16
1691 1 Port 18 State R Uint16
1692 1 Port 19 State R Uint16
1693 1 Port 20 State R Uint16
1694 1 Port 21 State R Uint16
1695 1 Port 22 State R Uint16
1696 1 Port 23 State R Uint16
1697 1 Port 24 State R Uint16
1698 1 Port 25 State R Uint16
1699 1 Port 26 State R Uint16
169A 4 Port 1 Statistics – Number of packets received R Uint64
169E 4 Port 2 Statistics – Number of packets received R Uint64
16A2 4 Port 3 Statistics – Number of packets received R Uint64
16A6 4 Port 4 Statistics – Number of packets received R Uint64
16AA 4 Port 5 Statistics – Number of packets received R Uint64
16AE 4 Port 6 Statistics – Number of packets received R Uint64
16B2 4 Port 7 Statistics – Number of packets received R Uint64
16B6 4 Port 8 Statistics – Number of packets received R Uint64
16BA 4 Port 9 Statistics – Number of packets received R Uint64
16BE 4 Port 10 Statistics – Number of packets received R Uint64
16C2 4 Port 11 Statistics – Number of packets received R Uint64
16C6 4 Port 12 Statistics – Number of packets received R Uint64
16CA 4 Port 13 Statistics – Number of packets received R Uint64
16CE 4 Port 14 Statistics – Number of packets received R Uint64
16D2 4 Port 15 Statistics – Number of packets received R Uint64
16D6 4 Port 16 Statistics – Number of packets received R Uint64
16DA 4 Port 17 Statistics – Number of packets received R Uint64
16DE 4 Port 18 Statistics – Number of packets received R Uint64
16E2 4 Port 19 Statistics – Number of packets received R Uint64
16E6 4 Port 20 Statistics – Number of packets received R Uint64
16EA 4 Port 21 Statistics – Number of packets received R Uint64
16EE 4 Port 22 Statistics – Number of packets received R Uint64
16F2 4 Port 23 Statistics – Number of packets received R Uint64
16F6 4 Port 24 Statistics – Number of packets received R Uint64
16FA 4 Port 25 Statistics – Number of packets received R Uint64
16FE 4 Port 26 Statistics – Number of packets received R Uint64
1702 4 Port 1 Statistics – Number of packets sent R Uint64
1706 4 Port 2 Statistics – Number of packets sent R Uint64
170A 4 Port 3 Statistics – Number of packets sent R Uint64
170E 4 Port 4 Statistics – Number of packets sent R Uint64
1712 4 Port 5 Statistics – Number of packets sent R Uint64
1716 4 Port 6 Statistics – Number of packets sent R Uint64
171A 4 Port 7 Statistics – Number of packets sent R Uint64
171E 4 Port 8 Statistics – Number of packets sent R Uint64
1722 4 Port 9 Statistics – Number of packets sent R Uint64
1726 4 Port 10 Statistics – Number of packets sent R Uint64
172A 4 Port 11 Statistics – Number of packets sent R Uint64
172E 4 Port 12 Statistics – Number of packets sent R Uint64
1732 4 Port 13 Statistics – Number of packets sent R Uint64
1736 4 Port 14 Statistics – Number of packets sent R Uint64
173A 4 Port 15 Statistics – Number of packets sent R Uint64
173E 4 Port 16 Statistics – Number of packets sent R Uint64
1742 4 Port 17 Statistics – Number of packets sent R Uint64
1746 4 Port 18 Statistics – Number of packets sent R Uint64
174A 4 Port 19 Statistics – Number of packets sent R Uint64
174E 4 Port 20 Statistics – Number of packets sent R Uint64
1752 4 Port 21 Statistics – Number of packets sent R Uint64
1756 4 Port 22 Statistics – Number of packets sent R Uint64
175A 4 Port 23 Statistics – Number of packets sent R Uint64
175E 4 Port 24 Statistics – Number of packets sent R Uint64
1762 4 Port 25 Statistics – Number of packets sent R Uint64
1766 4 Port 26 Statistics – Number of packets sent R Uint64
176A 4 Port 1 Statistics – Number of bytes received R Uint64
176E 4 Port 2 Statistics – Number of bytes received R Uint64
1772 4 Port 3 Statistics – Number of bytes received R Uint64
1776 4 Port 4 Statistics – Number of bytes received R Uint64
177A 4 Port 5 Statistics – Number of bytes received R Uint64
177E 4 Port 6 Statistics – Number of bytes received R Uint64
1782 4 Port 7 Statistics – Number of bytes received R Uint64
1786 4 Port 8 Statistics – Number of bytes received R Uint64
178A 4 Port 9 Statistics – Number of bytes received R Uint64
178E 4 Port 10 Statistics – Number of bytes received R Uint64
1792 4 Port 11 Statistics – Number of bytes received R Uint64
1796 4 Port 12 Statistics – Number of bytes received R Uint64
179A 4 Port 13 Statistics – Number of bytes received R Uint64
179E 4 Port 14 Statistics – Number of bytes received R Uint64
17A2 4 Port 15 Statistics – Number of bytes received R Uint64
17A6 4 Port 16 Statistics – Number of bytes received R Uint64
17AA 4 Port 17 Statistics – Number of bytes received R Uint64
17AE 4 Port 18 Statistics – Number of bytes received R Uint64
17B2 4 Port 19 Statistics – Number of bytes received R Uint64
17B6 4 Port 20 Statistics – Number of bytes received R Uint64
17BA 4 Port 21 Statistics – Number of bytes received R Uint64
17BE 4 Port 22 Statistics – Number of bytes received R Uint64
17C2 4 Port 23 Statistics – Number of bytes received R Uint64
17C6 4 Port 24 Statistics – Number of bytes received R Uint64
17CA 4 Port 25 Statistics – Number of bytes received R Uint64
17CE 4 Port 26 Statistics – Number of bytes received R Uint64
17D2 4 Port 1 Statistics – Number of bytes sent R Uint64
17D6 4 Port 2 Statistics – Number of bytes sent R Uint64
17DA 4 Port 3 Statistics – Number of bytes sent R Uint64
17DE 4 Port 4 Statistics – Number of bytes sent R Uint64
17E2 4 Port 5 Statistics – Number of bytes sent R Uint64
17E6 4 Port 6 Statistics – Number of bytes sent R Uint64
17EA 4 Port 7 Statistics – Number of bytes sent R Uint64
17EE 4 Port 8 Statistics – Number of bytes sent R Uint64
17F2 4 Port 9 Statistics – Number of bytes sent R Uint64
17F6 4 Port 10 Statistics – Number of bytes sent R Uint64
17FA 4 Port 11 Statistics – Number of bytes sent R Uint64
17FE 4 Port 12 Statistics – Number of bytes sent R Uint64
1802 4 Port 13 Statistics – Number of bytes sent R Uint64
1806 4 Port 14 Statistics – Number of bytes sent R Uint64
180A 4 Port 15 Statistics – Number of bytes sent R Uint64
180E 4 Port 16 Statistics – Number of bytes sent R Uint64
1812 4 Port 17 Statistics – Number of bytes sent R Uint64
1816 4 Port 18 Statistics – Number of bytes sent R Uint64
181A 4 Port 19 Statistics – Number of bytes sent R Uint64
181E 4 Port 20 Statistics – Number of bytes sent R Uint64
1822 4 Port 21 Statistics – Number of bytes sent R Uint64
1826 4 Port 22 Statistics – Number of bytes sent R Uint64
182A 4 Port 23 Statistics – Number of bytes sent R Uint64
182E 4 Port 24 Statistics – Number of bytes sent R Uint64
1832 4 Port 25 Statistics – Number of bytes sent R Uint64
1836 4 Port 26 Statistics – Number of bytes sent R Uint64

Interpreting the Port State Value

This section provides information for determining the port state.

In the following table, the upper byte repressents the interface state, and the lower byte represents the line protocol state.

Address

Description

Value

0x1700 to 0x171B

Port state information

Upper byte:

  • 0x0: Interface is down

  • 0x1: Interface is going down

  • 0x2: Interface is in the initializing state

  • 0x3: Interface is coming up

  • 0x4: Interface is up and running

  • 0x5: Interface is reset by the user

  • 0x6: Interface is shut down by the user

  • 0x7: Interface is being deleted

The lower byte:

  • 0x0: Line protocol state is down

  • 0x1: Line protocol state is up

Configure MODBUS

By default, the MODBUS TCP server listens for client requests on TCP port 502. The server is disabled by default. If enabled, the server uses this port unless another port is configured for MODBUS communications.

Follow these steps to configure MODBUS.

Before you begin

  • Firewall or security services enabled: TCP port might be blocked, preventing communication between the switch and client.

  • Firewall or security services disabled: Risk of denial-of-service attack on the switch.

  • Security for MODBUS TCP: Configure an ACL for traffic from specific clients or set QoS to rate-limit traffic.

Procedure

Step 1

Use the configure terminal command to enter the global configuration mode:

Example:

Device# configure terminal

Step 2

Use the scada modbus tcp server command to enable MODBUS TCP on the switch.

Example:

Device(config)# scada modbus tcp server

Note

 

A warning message will appear indicating that starting the MODBUS TCP server is a security risk. You must confirm by entering yes to proceed.

Tip

 

Use the no scada modbus tcp server command to disable MODBUS on the switch and return to the default settings.

Step 3

(Optional) Use the scada modbus tcp server port tcp-port-number command to set the TCP port to which clients send messages.

Example:

Device(config)# scada modbus tcp server port 600

The tcp-port-number can range from 1 to 65535. The default is 502.

Step 4

(Optional) Use the scada modbus tcp server connection connection-requests command to set the number of simultaneous connection requests sent to the switch.

Example:

Device(config)# scada modbus tcp server connection 4

The range for connection-requests is 1 to 5. The default is 1.

Step 5

Use the end command to return to privileged EXEC mode:

Example:

Device(config)# end

View MODBUS Information

Use the listed commands to view information for MODBUS.

Command

Purpose

show scada modbus tcp server

Displays information and statistics about the MODBUS server.

show scada modbus tcp server connections

Shows information and statistics for each client connection

clear scada modbus tcp server statistics

Clears all statistics for the MODBUS server, including those for each client connection.

Example 

Switch# show scada modbus tcp server
                Summary: enabled, running, process id 142
                Conn Stats: listening on port 801, 4 max simultaneous connections
                0 current client connections
                0 total accepted connections, 0 accept connection errors
                0 closed connections, 0 close connection errors
                Send Stats: 0 tcp msgs sent, 0 tcp bytes sent, 0 tcp errors
                0 responses sent, 0 exceptions sent, 0 send errors
                Recv Stats: 0 tcp msgs received, 0 tcp bytes received, 0 tcp errors
                0 requests received, 0 receive errors