Converting a PLC 2/17-Is a BTW (Block Transfer Read) Just a PLC 2 thing ?

[Baker in Virginia]

Good Evening ,

I need to convert a PLC 2/17 ( RS Logix 5 ) over to a CompactLogix 1769-L33ER . I took notice in the RS Logix 5 program that it has a few BTR and BTW instructions . What are these instructions usually used for ? Is it something mainly used in the RS Logix 5 platform ?

Also , the copy of the program that I have , in the instruction , the "Setup Screen" at the bottom doesn't open. "No Modules Exist in the IOConfiguration for this R/G/M " . What does this mean ? I select IO Configuration , and I don't see any I/O listed .

Thanks so much ,

 

[GaryS]

I will see if i can help a little
R/G/M is addressing Rack Number / Group (0-7) / Module (0-1)
each group is 16 Bits 8 Bits per module 0 is 0-7 1 is 8_15
or they can be setup with 16 bit modules example inputs on 0 and outputs on 1

having said that you say you have a PLC2/17 and you are using RS Logix 5 software
they don't work together for the PLC2's you use the ICOM or AB PLC2 Software
the RS Logix 5 Software is for the PLC5 series controllers
as for the BTW and BTR they are Block Transfer functions those have been replaced with messaging functions used to transfer blocks of data between the processor and some modules in the rack setup configuration and I/O Data
Some modules require a number of BTW's to set them up
with out the manual for each module it will be difficult to copy them to a ne processor
for the PLC2's you don't have a I/O list the I/O data is setup in the processor memory Ii (I would have to look it up again it's been a long time but) Output addressing would be word 0000-0700 and Inputs would be 1000-1700 R/G/M
if you are doing a conversion from a PLC2 I would recommend that you convert directly to a Logix Processor in some cases you may be able to keep the existing I/O Racks
I have done a few conversions and it's a job
Good Luck you are going to need it

 

[pal]

As an interim step , PLC5 has BTR (block transfer read) and BTW (block transfer write) instructions and information about these instructions for PLC5 and RSL5 is easier to find and understand . As Gary replied , it depends on what is on the other end of the communications . If it is an HMI then it is not so bad .

 

[Baker in Virginia]

Thanks Gentlemen ,

I appreciate the detailed information I'm excited about converting this to a CompactLogix -L33ER .

Thanks again.

 

[Ken Roach]

Because you are likely to have numerous questions during this conversion, it might be helpful to link new readers to a master post that includes the background information.

I think it's this one: PLC-5/11 *.RSP file best way to open


PLC-2 controllers date back to the early 1980's. Because PLC-5 controllers re-used the Bulletin 1771 chassis and I/O system, it was common to migrate PLC-2 to PLC-5 in the 1990's and early 2000s.

Block transfers do go back to the PLC-2 era; it's how they got more than 8 bits of data to and from an I/O module.

The BTR and BTW instructions in a PLC-5 include an a control block (that's where the .EN and .DN and .ER bits are) as well as the rack/group/slot address of the module, as well as a Data File block to hold the source or destination information.

RSLogix 5 provided a helpful structured way to configure and interpret the data files involved in a BTR or BTW. You would select a block transfer module from a list, and give RSLogix the starting addresses for the data files, and RSLogix would create the BTR or BTW with the correct arguments, and present drop-down menus and labeled fields for the module's parameters and data.

But if you never set up RSLogix 5 to do that, all it knows is the raw data file numbers. It doesn't have "IOConfiguration setup" data in the RSLogix 5 project file.

So you probably have to do some reverse engineering on this.

The first step, of course, is to find out for sure what kind of I/O module is installed. RSLogix 5 and RSLinx can't easily query it to find out like the ControlLogix platform can. Powering down and examining the labels on the side of the module is the main way to be certain, though a photo of the front often gives good clues.

 

[Ken Roach]

From those programs:

HFIELD includes two block transfer modules:

Rungs 0 and 1 address the module in Slot 03
BTR N7:40, Length 12
BTW N7:10, Length 21

Rungs 107 and 108 address the module in Slot 04
BTR N7:80, Length 5
BTW N7:60, Length 13

PENMAR includes one block transfer module:

Rungs 0 and 1 address the module in Slot 04
BTR N7:40, Length 5
BTW N7:10, Length 7


The BTR length of 5 suggests that two of these might be 1771-OFE analog output modules.

(more later, gotta walk the dogs)

 

[Ken Roach]

On further examination, I retract the guess of 1771-OFE for the Slot 4 modules. Inferring the identity of a block transfer module from the BTR/BTW sizes and the use of that data in the program is not always easy.

Examining the PENMAR program:

The 5-word Block Transfer Read block is stored in N7:40-44.

N7:40/0 is used to condition the BTW for that module in the next rung.
That suggests strongly that the first bit of the first word is a "Powerup"
indication that will stay =1 until a valid configuration BTW is sent to the module. That's typical of analog Input modules like the 1771-IFE.

N7:41 and N7:42 are only used in other discrete logic, suggesting that they are also status bits, rather than analog input data. If that module were a 1771-IFE, those bits would indicate under-range or over-range for Channel 1.

N7:43 is not used anywhere.

N7:44 has a decimal value of 29, and is compared to other Integer values several places in the program.

The 7-word Block Transfer Write block in the PENMAR program is sourced from N7:10-16.

And that data isn't used in any ladder logic. That suggests the values must be configuration data, not analog output data.

The bits in the third write word might be RTS and scaling, and the value 368 in the seventh word might be the maximum scaled input value.

So *maybe* it's a 1771-IFE, using only Channel 1.

 

[Baker in Virginia]

Wow! Thank you so much , Mr. Roach. Would you say that BTW's and BTR's are
no longer needed in that method , and MSG instructions are used , like GaryS had said ? I did take notice of an instruction FAL . Just one more question . What are FAL instructions used for ?

Thanks again . I appreciate it so much.

 

[Ken Roach]

If you are going to replace the PLC-5/11 controllers with a 1771-ASB and retain the chassis and I/O modules, you would also have to use a RIO scanner (AB-ANX or 1756-DHRIO). In that case, you would use MSG instructions instead of BTR or BTW instructions.

But if you're moving these signals to another I/O platform (presumably 1769 Compact I/O), you will not use those instructions. You'll just configure the I/O modules in Studio 5000 and re-scale the instructions that deal with their data.

FAL instructions are used to perform a function on an range of elements in a data table or a tag.

The PENMAR logic uses a similar-looking series of boolean logic operations in rungs 16-22 that operates on N7:2.

The HFIELD logic uses FAL to do something similar to three words at a time.

Do you have an idea of what that logic is *supposed* to do ?

 

[Baker in Virginia]

Thanks Sir,

No I don't . I need to go to the site this week , and will learn more about the project .

Thanks again , and have a great week.