Handling Network Addresses at Switchover

Overview

The following material describes handling network addresses at switchover. A Quantum Hot Standby system can communicate data over different network protocols:

Modbus
Modbus Plus
TCP/IP

WARNING

UNEXPECTED EQUIPMENT OPERATION

Offset address must not be assigned to another device than the peered PLC of the Hot Standby system.

Failure to follow these instructions can result in death, serious injury, or equipment damage.

In Hot Standby applications, correct address assignment must be fulfilled for proper operation of network address swap at switchover.

Swapping Modbus Addresses at Switchover

In a Quantum Hot Standby system, the Modbus port addresses are:

primary CPU: 1-119
standby CPU: offset +128
maximum address: 247
range 1-247

The Modbus port addresses can be changed using one of 2 methods:

communication menu in the front panel keypad
Modbus port tab in the Control Expert editor

Changing addresses:

Using the Communication Menu in the Front Panel Keypad
Change address on either:
Primary CPU: Access the front panel keypad of the primary CPU. Go to the Communication menu. Go to the Serial Port submenu. Select the address. Change the address. Perform the application program transfer. Verify that the standby CPU Modbus address is +128.	Standby CPU: Access the front panel keypad of the standby CPU. Go to the Communication menu. Go to the Serial Port submenu. Select the address. Change the address. Perform the switchover. Ensure that the standby CPU switched to the primary CPU. Perform the application program transfer. Verify that the standby CPU Modbus address is +128.
Using the Modbus Port Tab in Control Expert Editor
To change the address, download the application program.
Note: If the Modbus address is changed in the primary CPU using the front panel keypad, ensure that the application program transfer is made to enable the corresponding Modbus switchover in the standby CPU.

NOTE: In a Quantum Hot Standby system, only one port is available for Modbus.

By default, there is an address swap at switchover between the primary CPU and the standby CPU Modbus ports. This default condition can be changed using the following 2 methods:

Use the Hot Standby menu in the Control Expert editor.

This choice requires the application program to be downloaded.
Use the Command Register system bit %SW60.8.

This choice must be performed online in the primary CPU.

Selecting/deselecting address swap at switchover:

Using Hot Standby Menu in Editor	Using the Command Register system Bit %SW60.8
Open the Hot Standby menu in Control Expert. Go to the Swap Address at the switchover area. Deselect Modbus Port 1. Verify the modifications. Download the application program to the controller. Perform the switchover. Ensure that the standby CPU switched to the primary CPU. Perform the application program transfer.	Connect to the primary CPU. Access the Command Register System bit %SW60.8. Set the bit to 1. The default is 0.
When a switchover occurs: If you change the options, the port addresses are not affected until the switchover occurs. If NOM modules are used in the configuration, the offset of the Modbus Plus address is +/-32 after the Modbus Plus address switchover.

Switchover with swapping Modbus addresses:
- If controller A is the primary CPU controller and its Modbus port has an address of 1, then the default addresses for the comparable port on controller B, the standby CPU, is 129, which is 1 plus the offset of 128.
- If controller B becomes the primary CPU controller as the result of a switchover, its Modbus port assumes the address of 1, and the comparable port on controller A assumes the address of 129.
Switchover without swapping Modbus addresses:
- If controller A is the primary CPU controller and its Modbus port 1 address is 1, then that port address remains at 1 after the switchover occurs. Likewise, if controller B becomes the primary CPU controller as a result of a switchover, its Modbus port 1 address is 129.

Swapping Modbus Plus Addresses at Switchover

In a Quantum Hot Standby system, the Modbus Plus port addresses on the standby CPU controller are offset +/-32 from the comparable ports on the primary CPU controller.

Modbus Plus address swap behavior at switchover:

Default behavior before switchover:

controller A = primary CPU

Modbus Plus address = 1
controller B = standby CPU

Modbus Plus address = 33 (1 +32)

(+32 = offset)

After switchover occurs:

controller A = new standby CPU

Modbus Plus address = 33 (1 +32)
controller B = new primary CPU

Modbus Plus address = 1

NOTE: Numerical address of both ports (A and B) range: 1 - 64.

If the primary CPU address = 50, the corresponding standby CPU = 18 (50 - 32).

The Modbus Plus address of the controllers can be changed using the front panel keypad: Communication → Modbus Plus → Modify Address.

NOTE: The Modbus Plus port will be inactive for approximately 10 seconds after the RUN standby CPU state is shown on the LCD display.

Modbus Plus address swap behavior when the address is changed:

Forced behavior before switchover:

controller A = primary CPU

Modbus Plus address = 1
controller B = standby CPU

Modbus Plus address = 33 (1 + 32)

(+32 = offset)

Change address of primary CPU = 5:

controller A = primary CPU

Modbus Plus address = 5
controller B = standby CPU

Modbus Plus address = 33

Transfer application program:

controller A = primary CPU

Modbus Plus address = 5
controller B = standby CPU

Modbus Plus address = 37 (5 + 32)

Force switchover:

controller A = new standby CPU

Modbus Plus address = 37 (5 + 32)
controller B = new primary CPU

Modbus Plus address = 5

If the Modbus Plus address is modified, perform an application program transfer. If not performed, a transfer creates a different offset address in the standby CPU.

NOTE: At switchover, the Quantum Hot Standby system and NOM modules swap Modbus Plus addresses almost instantaneously (within one or two milliseconds). This almost instantaneous switchover means that the host devices, which are polling the controller, must be talking to the primary CPU controller and that the network should have minimal network interruption during switchover.

NOTE: When using Modbus Plus communication and OSLoader, only address 1 is valid.

Swapping NOE/NOC IP Addresses at Switchover

When used in a Quantum Hot Standby system, the Quantum Ethernet TCP/IP network modules 140 NOE 771 •1 and 140 NOC 78• 00 support address swapping at switchover. The swapping of IP addresses behaves much like the address swap of the Modbus Plus ports, except that the offset is 1 instead of 32.

At switchover, the modules exchange their IP addresses. 140 NOE 771 •1 and 140 NOC 78• 00 address swapping occurs automatically and can not be controlled by options selected in any of the tabs of the editor or controlled by turning ON/OFF any of the bits in the command register.

All standard rules apply to IP addressing with the additional restriction that the IP address cannot be greater than 253 or the broadcast address minus 2. Also, no other device should be assigned the IP address configured in Control Expert +1.

NOTE:

For 140 NOE 771 •1 and 140 NOC 78• 00 address swaps:

140 NOE 771 •1 are the only Ethernet option modules that support the IP address swap in Quantum Hot Standby with Unity Pro V2.0.

Unity Pro is the former name of Control Expert for version 13.1 or earlier.
140 NOE 771 •1 and 140 NOC 78• 00 modules must be configured in the same slot of the primary CPU and standby CPU backplanes.
140 NOE 771 •1 modules require a minimum firmware revision 2.0 or higher.

Quantum EIO Module IP Addresses at Switchover

The Quantum EIO module IP addresses are assigned to the 140CRP31200_A and 140CRP31200_B remote I/O head modules when the Hot Standby system is first configured. During a switchover, their IP addresses do not change.

The 140NOC78•00 module IP addresses change from IP to IP+1 during switchover from primary to standby.