1756 ControlLogix v13 Download Cause Outputs To Turn Off If Saved On?

Hi All,
I have a ControlLogix PLC with v13. The client requires to swap 1756-OB16 module with 1756-OB32 module. From documentation, I have found so far that the v13 is not hot swappable. So this will require a download to the PLC. What I am unable to find is, if I have an existing output turned 'ON' for let's say slot 8 OB16 DO card @ channel 0, then when I save the program it will upload all tag values.
After that I do the swap at slot 8 with OB32 module. When I download the program to the PLC, will the channel 0's output be left ON or will it turn OFF for a scan and then ON?
Thanks.

I did a quick test with v19 controller I had lying around. It turned off the output and then turned it on. So I guess everything will turn off and then turn on depending on logic.

When you download, the controller must switch to Program mode. The output will do whatever it was configured to do. In the I/O configuration for the output module there is a setting for what you want each individual output to do when the controller is switched to Program mode. On, Off, or Hold last state.

Be aware though of the prescan state of all OTE style outputs. The controller, by default resets all OTE outputs during the prescan sequence.

OG

Operaghost said:

When you download, the controller must switch to Program mode. The output will do whatever it was configured to do. In the I/O configuration for the output module there is a setting for what you want each individual output to do when the controller is switched to Program mode. On, Off, or Hold last state.

Be aware though of the prescan state of all OTE style outputs. The controller, by default resets all OTE outputs during the prescan sequence.

OG

Click to expand...

Good explanation. Just a little addition...

Yes, as explained, you have a choice as to what each output's state will be set to when the controller is taken out of Run Mode. Just to be clear on what exactly is in control during this operation...

When transitioning from Run Mode to Program Mode the output module takes control of the outputs and applies the configured setting. When transitioning from Program Mode to Run Mode the controller takes control of the outputs at which point the prescan may cause a bump on any outputs addressed to OTE instructions.

If you are configuring the outputs for On or Hold Last State, and you want to avoid this bump, then you can consider using the Output Latch (OTL) instruction instead of the Output Energize (OTE) instruction. The OTL instruction is not modified during the prescan and so will provide a bumpless transition.

Just to point out, in case any novices are reading this, if you use the OTL instruction to energize an output, then you will need to use an Output Unlatch (OTU) instruction to de-energize the output.

Regards,
George

anthr_plcnewbie said:

Hi All,
I have a ControlLogix PLC with v13. The client requires to swap 1756-OB16 module with 1756-OB32 module. From documentation, I have found so far that the v13 is not hot swappable. So this will require a download to the PLC. What I am unable to find is, if I have an existing output turned 'ON' for let's say slot 8 OB16 DO card @ channel 0, then when I save the program it will upload all tag values.
After that I do the swap at slot 8 with OB32 module. When I download the program to the PLC, will the channel 0's output be left ON or will it turn OFF for a scan and then ON?
Thanks.

Click to expand...

The problem you will have is that you cannot "change" an I/O module, you have to delete the existing, and insert a new module of the type you want. Of course this has to be done offline.

Deleting the existing module will erase the controller tags for the module, inserting the new module will create new tags. These tags will have zero data in all fields.

Regardless of what you do, the new module will have no knowledge of the old module's output states, it is a new module that can't inherit what the previous module was configured to do. It will wait for the configuration tag to be downloaded, so will always "power up" with the outputs OFF.

There is no way in this scenario that the new output module can retain any status that the previous module had.

But I can't see why you want this functionality, and have to ask this question - surely your logic should decide which outputs will be "on" on its first scan ??? It is not a cleverly written program if it can't survive a power-loss or mode-change from program to run.

Operaghost said:

When you download, the controller must switch to Program mode. The output will do whatever it was configured to do. In the I/O configuration for the output module there is a setting for what you want each individual output to do when the controller is switched to Program mode. On, Off, or Hold last state.

Be aware though of the prescan state of all OTE style outputs. The controller, by default resets all OTE outputs during the prescan sequence.

OG

Click to expand...

You have assumed the output module hasn't lost power. In the OP's scenario he has to change the module, so the new module will be unconfigured at power-on.

Doesn't the physical module need to be changed and all of the outputs rewired? You are changing from a 1756-OB16 to OB32. I maybe missing something but these are the steps that should be followed:
1. Stop machine/process and place it in a safe state.
2. Save program and upload all values.
3. Go offline and swap out module in I/O tree and readdress the outputs in the logic if the module name has changed.
4. Power off panel and swap module and move terminations.
5. Power on panel.
6. Download new program and place in run mode.
7. Validate all moved outputs before attempting to restart normal operation.