140 NOE 771 x1 / 140 NOC 78• 00 Operating Modes in Quantum Hot Standby System
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Operating Modes
The 140 NOE 771 x1 / 140 NOC 78• 00 module modes are:
The Quantum Hot Standby and the 140 NOE 771 x1 / 140 NOC 78• 00 operating modes are synchronized by these conditions:
CPU Module Status
Hot Standby State
140 NOE 771 x1 / 140 NOC 78• 00 Operating Mode
present and healthy
primary CPU
primary
present and healthy
standby CPU
standby
present and healthy
offline
offline
present and healthy
unassigned
standalone
Not present or unhealthy
N/A
standalone
Any of the following events affect the 140 NOE 771 x1 / 140 NOC 78• 00 operating mode:
IP Address Assignment at Power-Up
A 140 NOE 771 x1 / 140 NOC 78• 00 module obtains its IP address assignment at power-up as follows:
If the Hot Standby state is...
Then the IP address assigned is...
unassigned
Default IP address
primary CPU
IP address configured in Control Expert
standby CPU
IP address configured in Control Expert + 1
unassigned to offline transition
See the Offline Mode at Power-up Sequence topic in the next table.
If two 140 NOE 771 x1 / 140 NOC 78• 00 modules power-up simultaneously, then:
Offline Mode at Power-up Sequence
Result
Controller A powers up before controller B.
  • IP address of controller A is the IP address configured in Control Expert.
  • IP address of controller B is the IP address configured in Control Expert + 1.
Both controller A and controller B power up at the same time.
The resolution algorithm assigns the configured IP address to controller A, and it assigns the configured IP address + 1 to controller B.
The 140 NOE 771 x1 / 140 NOC 78• 00 module detects a duplicate IP address, the IP address remains at the default IP and the 140 NOE 771 x1 / 140 NOC 78• 00 module blinks a diagnostic code.
If no IP configuration exists, 140 NOE 771 x1 / 140 NOC 78• 00 modules remains in the standalone mode. The IP address must be obtained for the:
Ethernet Services at Power Up
The following table shows how the status of a 140 NOE 771 x1 / 140 NOC 78• 00 module’s service is affected by the Quantum Hot Standby state:
Hot Standby State
Status of 140 NOE 771 x1 / 140 NOC 78• 00 Services
Client Services
Client/Server Services
Server Services
EIP Scanner
Global Data
Modbus/EIP Messaging
FTP
SNMP
HTTP
unassigned
not running
run
run
run
run
run
primary CPU
run
run
run
run
run
run
standby CPU
stop
stop
run
run
run
run
offline
stop
stop
run
run
run
run
Hot Standby Switchover
The following table describes how the 140 NOE 771 x1 / 140 NOC 78• 00 modules coordinate a Hot Standby switchover. The 140 NOE 771 x1 module is used as the example in the following procedure.
Step
Action
1
In a Hot Standby configuration NOE A is running in the primary PLC and NOE B is in the standby PLC.
2
NOE A detects that its PLC has changed from primary CPU to the offline mode.
3
NOE A changes from primary NOE to offline with the same Ethernet services running and starts its watchdog timer (with a 500 ms time-out setting). It waits for a message to swap IP addresses from NOE B.
4
NOE B detects that its PLC has changed state from standby PLC to primary CPU.
5
NOE B stops all its Ethernet services, sends a request to NOE A for the synchronization of the IP address swap, starts its watchdog timer (with a 500 ms time-out setting) and waits for a response from NOE A.
6
When NOE A receives the request from NOE B (or after the NOE A watchdog timer times out), it stops all its Ethernet services:
  • If it has received a request, NOE B sends a response to NOE A.
  • If its watchdog timer has timed out, NOE B does not send a response.
NOE A then swaps its IP address and starts the secondary services.
7
NOE B swaps IP addresses and starts Ethernet services as the primary NOE.
8
After NOE A senses that its local CPU changes from offline to standby, it takes the secondary IP address.
9
NOE B now becomes the primary NOE.
10
NOE B opens all client connections, listens for all server connections, and reestablishes those connections.
11
NOE A listens for all server connections and reestablishes those connections.
NOTE: During the Hot Standby switchover, there is a loss of communication during 500 ms between the PLC and the HMI and/or Control Expert.
Going to Offline
When either the CPU stops or the Hot Standby CPU goes to offline mode, 2 events occur:
  1. the 140 NOE 771 x1 / 140 NOC 78• 00 module goes to the offline mode
  2. the 140 NOE 771 x1 / 140 NOC 78• 00 module uses the IP address of the present configuration
The IP address assignment when going offline:
Hot Standby State
IP Address Assigned Is...
primary CPU to offline
configured IP address, if other controller does not go to primary CPU mode
standby CPU to offline
configured IP address + 1
NOTE: For more information, refer to the 140 NOE 771 x1 / 140 NOC 78• 00 IP Address Assignment topic.