Starting an M580 Hot Standby System

Preconditions

During the start-up sequence, each PAC is assigned a Hot Standby state (Primary, Standby, or Wait) according to the:

State of the Ethernet remote I/O network
State of the Hot Standby link
A/B/Clear rotary switch position
Operating state (Run or Stop) of the CPU

On initial start-up, confirm that the:

Hot Standby link is connected.
PAC you start first has been fully programmed.
A/B/Clear rotary switches on the back of the two Hot Standby CPUs are set to different positions: one to “A”, the other to “B”.

NOTE: The first controller to power up becomes the primary controller, regardless of its designation as A or B.

Starting the Hot Standby System

The following chart provides the appropriate steps for starting your Hot Standby system.

Step	Action
1	Turn on power to the first backplane. NOTE: In this example, this is the backplane with the controller A/B/Clear rotary switch position set to “A”.
2	Connect your PC with both Control Expert and the program you want to download.
3	Download the program to the controller.
4	Start the controller in that backplane. If all necessary preconditions exist, the controller becomes the primary Hot Standby CPU.
5	Turn on power to the second backplane. NOTE: In this example, this is the backplane with the controller A/B/Clear switch set to “B”.
6	If necessary, repeat steps 2 and 3 for the second controller, and download the program to it. NOTE: If the second controller is not configured, the primary CPU automatically downloads the program to the second controller, which becomes the standby.
7	Start the second controller.
8	Check the LED display for each CPU. If both CPUs are operating as intended, the LEDs will appear as follows:
	LED	First CPU (A)	Second CPU (B)
	RUN	Solid Green	Solid Green
	REMOTE RUN	Solid Green	Solid Green
	ETH MS	Solid Green	Solid Green
	ETH MS	Solid Green	Solid Green
	A	Solid Green	OFF
	B	OFF	Solid Green
	PRIM	Solid Green	OFF
	STBY	OFF	Solid Green
	SRUN (safety PAC)	Solid Green	Solid Green
	SMOD (safety PAC)	Solid Green	Solid Green

NOTE: For a description of:

BMEH58•040 CPU LEDs, refer to LED Diagnostics.
Startup states of the BMEH58•040 CPU, refer to Hot Standby State Assignments.

A/B/Clear Rotary Switch Role Assignment

The A/B/Clear rotary switch assignment does not by itself determine the Hot Standby primary or standby role of a CPU. Typically, the first controller to power up becomes the primary controller, regardless of its designation as A or B; the secondary controller to power up becomes the standby.

The A/B rotary switch settings determine the role of a CPU only in the case of a simultaneous power up. In that case:

The CPU set to “A” becomes primary.
The CPU set to “B” becomes secondary.

Conflicting A/B/Clear Rotary Switch Role Assignment

If you mistakenly set the A/B/Clear rotary switch to the same setting – “A” or “B” – for both Hot Standby CPUs, the first CPU to power up becomes the primary, and the second CPU to power up enters wait state.

If you mistakenly set the A/B rotary switch to “Clear” for both CPUs, both CPUs remain non-configured.

This condition can be determined by examining the following LEDs for each CPU:

If both A/B CPU Switches set to:	LED	First CPU to power-up	Second CPU to power-up
A	A	Blink Green	Blink Green
	B	OFF	OFF
	PRIM	Blink Green	OFF
	STBY	OFF	OFF
B	A	OFF	OFF
	B	Blink Green	Blink Green
	PRIM	Blink Green	OFF
	STBY	OFF	OFF
Clear	A	Blink Green	Blink Green
	B	Blink Green	Blink Green
	PRIM	OFF	OFF
	STBY	OFF	OFF

NOTE: If the A/B rotary switches for both CPUs are set to the same position (“A” or “B”), and if both CPUs start-up simultaneously, both CPUs enter wait state.