Will program get deleted if i restart plc?

Hey everyone

I just want to know if the program residing in cpu gets erased if i cycle power with out battery. I am talking about ab plcs . When i checked the controller the battery led is not lit.Also, in rslogix 5K the battery is not highlighted .Where does the plc store its program? Why does it need a battery? Isn't plc like pc?

I just want to know if the program residing in cpu gets erased if i cycle power with out battery

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Yes, the program will be erased.
If an EPROM is installed, then the program will read from the EPROM at next powerup. However, various settings thatv are not stored on the EPROM will be lost.

When i checked the controller the battery led is not lit

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The BAT lamp will light if the battery is low or missing.

Isn't plc like pc?

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A typical PLC is like a PC that has "suspend" turned on. The EPROM in the PLC is like the HD in a PC.
If the battery is low in PLC or PC when the PLC/PC is tunred off, then the programs has to be loaded from the EPROM or HD.

1 Does it mean eprom and ram contain the different stuff.?
2 What if i make changes to program ,where does it get stored eprom or ram.

bornwild said:

1 Does it mean eprom and ram contain the different stuff.?
2 What if i make changes to program ,where does it get stored eprom or ram.

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Dynamic Data will be different in RAM compared to the EEPROM, or even the last time you saved the Program to your PC. This means changing values such as Tank Level, Carriage Position, which Pump is running etc will probably be different the next time you look.

When you make changes to a program, it is always in RAM. If you want them in the EEPROM, you have to specifically write them there.

I have seen a number of times where someone made a change to a PLC Program, and it disappears at the next Power Cycle. When they tell me that, I tell them to check for an EEPROM.

Stu.....

sthompson said:

Dynamic Data will be different in RAM compared to the EEPROM, or even the last time you saved the Program to your PC. This means changing values such as Tank Level, Carriage Position, which Pump is running etc will probably be different the next time you look.

When you make changes to a program, it is always in RAM. If you want them in the EEPROM, you have to specifically write them there.

I have seen a number of times where someone made a change to a PLC Program, and it disappears at the next Power Cycle. When they tell me that, I tell them to check for an EEPROM.

Stu.....

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@bold.
Suppose there is no eprom and you made changes to plc program and it is running for months then one day there is problem with plc and you have to cycle power that means i lose the changes i made.

bornwild said:

@bold.
Suppose there is no eprom and you made changes to plc program and it is running for months then one day there is problem with plc and you have to cycle power that means i lose the changes i made.

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There are very few problems that would require cycling the power on the PLC. If this is a common thing for you to do, we need to dig deeper.

To answer you question, if the Battery is good, no you will not lose your PLC Program changes. Once they are installed, they are the running Program, and reside in RAM. As long as the PLC is powered, you are fine. If the power shuts down for any reason, the RAM is maintained by the Backup Battery. The newer AB PLCs also have a large value Capacitor that will maintain the RAM for a while. This is to allow changing the Backup Battery, which is installed on the board, and you need to remove the Processor from the Chassis to change it.

Stu.....