toggled bit retained through power cycle?

sorry about this very basic question. I did a thread search but was unsuccessful.

So, my question. If I toggle a bit during a Run, and power loss happens, is the toggled bit retained? Saved by the battery?

Remember to list every time the PLC type you are using. You have discussed ControlLogix before so I'll go with that, but each system is different.

In ControlLogix, if the bit is not being affected as an output of any logic then it may be retained through a power cycle.

Hello,

It would help if you provided the PLC brand/model/memory area/etc.

Sorry for not listing the specific PLC model. The question was about Micrologix 1400, and the bit was just an internal coil bit. We have multiple process lines, and each line uses MLX1400 and same RSS file. Half of the lines have one clamp to hold material hoppers, and the rest of the lines have two clamps. An internal coil bit in the program tells the PLC how many clamps; toggle 1 = 2 clamps, and toggle 0 = 1 clamp. In the future we are going to upgrade to Controllogix PLC, so I would like to know whether the toggled bit is going to be retained for Contrologix as well.

A question to ask is - how mach damage would occur if the bit wasn't set right and the machine was run? If it's just an annoyance then go ahead and use the toggled bit method.

If it is more critical then dedicate a free input for indicating this on the machine. Wire it ON for one of the setups and OFF for the other. You can copy that input's state into the bit you currently have and make no other changes. Then there is no other step to take on downloading a program.

I don't think it is critical. But even so, should I trust the PLC (whether MLX1400 or CLX1500) to retain the toggled bit status through power cycles always? When I asked the programmer, he said that if the circuit loses power (intentionally or unintentionally), the PLC's battery will save the last states of the program, including the toggled bit status. I guess that is what you meant when you said CLX "may" save the toggled bit status. But would you suggest any situations that it may not?

If it's in Control Logix the bit will be retained on until you toggle it again. This is because the bit is not assigned as a output. ie (A push button on a HMI), No output just a input.

Hi,

>But would you suggest any situations that it may not?

Yeah, the battery is dead.

Sorry - "then it SHOULD be retained through a power cycle."

Most any conceivable loss of its status, given that it would not be the object of any logic or HMI changing operation, would probably affect enough to be detected as a major fault by the PLC operating system.

We always entrust changeable values to this type memory retention. I was just being cautious in my answer. But I still like the input option. I've used it where a customer had a number of 'close to identical' machines. I used such inputs to select the small differences in operation. It allowed the customer to only worry about one program.

S:fs

Use the controllers first scan bit, S:FS. This bit is only active on the first scan. I often use it in a main dispatch in order to dispatch to a power-up routine that only executes once on start up.

-
Al
theplchub.com