The system has been working well in the past.

but I could no longer replicate the same issue.

I am seeking assistance and would greatly appreciate a helpful response.

Giraffe0804

The PLC is an S7-400H (CPU-417-5H PN/DP) redundant system.

The system has been working well in the past.

However, today, when I turned the power on, the system did not start operating.

Even after turning the power off and on again, the system still did not function.

I had to press the Reset using the MRES on the CPU module,

and only then did the PLC start operating normally.

Upon examining the diagnostic buffer, it revealed a CPU STOP due to an I/O Error.

The summarized event message is as follows:

[snip]

Afterward, I attempted several power ON/OFF cycles,

but I could no longer replicate the same issue.

Even after reading related articles on this site, I have been unable to find a precise solution.

I am seeking assistance and would greatly appreciate a helpful response.

 Hello,

1. Please check the address setting by dip switched in Profibus slaves. If these addresses doesn't match HW config, it will lead to IO access error. In case somebody changed the dip switches during running, nothing will happen until  power cycle of controllers.

2. Tell us if you have RAM or Flash EPROM in CPU. In case of RAM and in case battery fault occured, you will need to re-download the program again to CPU.

Ayman Elotaify

 Hello,

1. Please check the address setting by dip switched in Profibus slaves. If these addresses doesn't match HW config, it will lead to IO access error. In case somebody changed the dip switches during running, nothing will happen until  power cycle of controllers.

2. Tell us if you have RAM or Flash EPROM in CPU. In case of RAM and in case battery fault occured, you will need to re-download the program again to CPU.

   The DP Slave Modules are IM153-2, and both modules are configured

   Furthermore, the Bus Address Setting has not been changed and is currently

   The specifications for the PLC are as follows (Fig. 1):

   - CPU Module: CPU-417-5H PN/DP

   - Power Module: PS 405 10A with 2 Backup Batteries

Does the "In case battery fault" you mentioned refer to the Backup Battery in the Power Module?

Could this be a potential cause of the issue?

Ayman Elotaify

  Hello,

1. Please check the address setting by dip switched in Profibus slaves. If these addresses doesn't match HW config, it will lead to IO access error. In case somebody changed the dip switches during running, nothing will happen until  power cycle of controllers.

2. Tell us if you have RAM or Flash EPROM in CPU. In case of RAM and in case battery fault occured, you will need to re-download the program again to CPU.

 Hello Mr. Ayman Elotaify,

For your reference, I have attached module data sheets for the CPU, Power Module, Memory Card, and Backup Battery.