AB PLC5 BTW/BTR Block

koyeap

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Join Date
Feb 2013
Location
Selangor
Posts
17
Dear Pros,

Need help on converting PLC5 to Studio 5000.:geek:
I found few BTW/BTR block pointing back to Rack 000, group 0, module 0, which should be the CPU module. The weird part is the length is 0. Is length 0 mean the BTW/BTR block not in use anymore?

Or this is actually some technique to get some hardware status?
Attached some print screen for the logic.

Print Screen 1.PNG Print Screen 2.PNG
 
The CPU in a PLC-5 system does not have a rack address. Rack 0, Group 0 Module 0 would be the first slot to the right of the CPU. The length of 0 means whatever that module has available (read) or will accept (write). It was a default setting for when you didn't want to have to look up the actual number of words to read or write. When managing memory, it meant that you had to assume it would use 64 words. You wouldn't just say 64 (the maximum) because if the module had less than that it would cause an instruction error. So using 0 was very common.

OG
 
Last edited:
It looks like they wrote the block transfer and then never actually finished
Length of 0
I believe the rack 0 and group 0 I. The processor
In logix5000 you need need to use messaging
 
The CPU in a PLC-5 system does not have a rack address. Rack 0, Group 0 Module 0 would be the first slot to the right of the CPU. The length of 0 means whatever that module has available (read) or will accept (write). It was a default setting for when you didn't want to have to look up the actual number of words to read or write. When managing memory, it meant that you had to assume it would use 64 words. You wouldn't just say 64 (the maximum) because if the module had less than that it would cause an instruction error. So using a length of 0 was very common.

OG

I've never had to quote myself before. Emphasis added.

OG
 
oh I see, thanks a lot! sorry i missed out the 0 is reserve for maximum in manual.

Next module to CPU is a backup comm module(BCM), which mean this block transfer is for redundancy data exchange purpose? or is connect to 3rd parties devices?
 
oh I see, thanks a lot! sorry i missed out the 0 is reserve for maximum in manual.

Next module to CPU is a backup comm module(BCM), which mean this block transfer is for redundancy data exchange purpose? or is connect to 3rd parties devices?

Since I am going to upgrade the PLC5 to 1756 Series, which mean if this is for redundancy purpose then i can ignore the BTW/BTR in new logic right?

Thanks
 
The BTR/BTW for the BCM modules was a method to transfer data from one CPU to another. All the remote I/O data was automatically transferred. It was a way to synchronize any other data between the two CPUs. But they are running identical programs so they should have the same data anyway. I never used this myself. To me it seemed unnecessary. But I'm sure someone can identify where they needed this.

This would be unnecessary in the ControlLogix. Synchronization of redundant systems is handled without the need for any logic messaging.

OG
 

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