1771-OFE2 read/write blocks in a PLC5

I was called in this morning (too dang early) to help troubleshoot a problem with some newly installed VFD's. We found that the 4-20mA signal was not coming in from the PLC. After some digging, I found the card had been in the rack for quite awhile but was never configured. I've never set up the read-write blocks for this type of card, does anyone have any ideas of where to start?

This is a PLC5/40C 16 slot rack, with a 1771-OFE2 installed in Slot 14, (Rack 1, Group 6) with the four analog outputs beginning with address N20:5.

Thanks for any help.

http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1771-um030_-en-p.pdf

First thing to do is set the dipswitches.

See pages 2-3 through 2-7

Next, you will need a BTW instruction to send configuration and channel data to the card repeatedly. Your block of BTW data will be 13 words of consecutive data to use all 4 channels. The BTR data will require 5 words. The BTR will report the raw DAC data and status bits back to the PLC.

The example starts on page 4-9.

I suggest you use a R control data type instead of the N type in the example.

If you are using RSLogix, and there are no block transfers already set up for that card, then you can use the wizard to create them for you. You just have to enter the addresses.

How can you tell if there are already instructions? Search for "BTW" and look at the rack and group numbers.

To create new BTR/BTW in the default form, use the I/O config to place the module in the correct location in RSLogix. Then double click it to initiate the wizard.

You will be prompted for the correct addresses and the rungs will be inserted as ram rung edits. You then review them and accept, test and assemble them to get the card talking.

Note that the scaling of the outputs is done inside the analog card. Once configured and talking, you can go to a setup page in RSLogix to make changes to those scaling values and setup bits in a more user friendly fashion. When you make edits on that screen, RSLogix will prompt you to do a "1 time" download of those changes. It will alter the data tables for you to make the changes "stick". You get to that setup screen by clicking the text "Setup Screen" at the bottom of the BTW or BTR instruction for the card.

This should get you a good start, but I don't have RSLogix5 to post screenshots.

Hope it helps,
Paul

OkiePC said:

I suggest you use a R control data type instead of the N type in the example.

Click to expand...

EDIT: I should have said use a BT type control word instead of N. (Thanks Ron B.)

let’s make sure that we’re on the same page here ... this is an existing system that has been functioning ok for some amount of time in the past ... is this correct? ... let’s assume for the purposes of discussion that your answer is “yes, the system has been working” ...



now then ... you said:

... I found the card had been in the rack for quite awhile but was never configured.

Click to expand...

I’m going out on a limb here, but I’ve got a hunch that by “never configured” you meant that the module doesn’t appear in the program’s “I/O Configuration” tables ... specifically, you don’t see the module listed anywhere when you go to this area of the software:

secret handshake: in the PLC-5 family, the modules do NOT have to be shown in the “I/O Configuration Table” in order to work properly ... specifically, don’t be confused by the fact that the module isn’t listed here - the system might still be able to function flawlessly in spite of that ...

I've never set up the read-write blocks for this type of card, does anyone have any ideas of where to start?

Click to expand...

if the module has already been working in the past, then chances are VERY GOOD that the block transfers are already installed ... simply put, the module could NOT have been functioning properly in the past without the block transfers ...



my distinguished colleague OkiePC has given you some good tips to use if you do indeed need to install the Block Transfers ... but I’m barking up another tree ... I’ve got a hunch that the Block Transfers are already there ... either something has scrambled the block transfers ... or something has scrambled the configuration data that the block transfers are supposed to use ... or the block transfers aren’t being scanned by the processor ... or something else is wrong with your system ...



of course all of this is speculation on my part - until we hear more details from you ... if all else fails, it would be a good idea to post your .RSP file ... the more we know, the more we can help ...



best guess from where I sit: when you couldn’t find the module listed in the I/O Configuration Table, you assumed that the omission was a part of your problem ... you would certainly not be the first to have made that incorrect assumption ... as I said earlier, the module does NOT have to be listed in order to work correctly ...



hope this helps - without just adding more confusion to the fire ...

Sorry for the confusion. The module is in the I/O configuration, but has never been wired to, and has no BTR or BTW blocks anywhere in logic.

What I meant by it being installed for a while, was that the card has been in the rack, but the I/O hasn't been used.

This morning I've gone into the I/O Configuration and used the BTR/W wizard and it appears to be functioning in logic. I need to verify this at the card and I may be in good shape.

ok ... we’ve got a much better picture now ...



you started out by asking for basic help with the Block Transfers, and OkiePC should have gotten you well on the way in that department ... here’s a quick screen shot along the “set up the module” lines in case you need help with that end of things ...







the areas highlighted in yellow are the most common settings - but naturally your application might need something different ... the “2048” data reading is just an example for a quick “50% = 12 mA” output signal on Channel 1 for testing purposes ...



apparently you’ve already found the “magic button” (circled in red) that automatically inserts the Block Transfer rungs for you ...



and here’s something that a lot of people skip over when they’re installing these things ...







you can read all about this feature in this manual but here’s just a quick preview in case you’re just wondering what the jumpers look like ...








good luck with your project ...

Thanks for the replies so far.


Now I have added the BTR/W blocks using the 'Insert Ladder Rungs' button procedure.

The problem I have now is the 'error' pin on both of the blocks is becoming active during the read and write.

When I go to the BT block DLEN word, I'm getting a '-9' back for each block.

The block transfer timeout, set in the instruction, timed out before completion.

Click to expand...

Is there a way to correct this, will I need to stop the processor and move, re-seat, or replace the card, or am I still missing something?

Note: RUN light is on solid (green), FAULT light is off

Thanks again.

can you post your .RSP file? ... or at least a screen shot of your Block Transfer rungs? ... are you SURE that you're using "one-slot" addressing? ... how are you sure? ... note: if the OFE module is located in the SAME chassis with the PLC-5 processor, then you can check the addressing mode in the "Processor Status" feature - on the "Switches" tab ... do NOT trust the addressing mode setting which is shown in the "I/O Configuration Table" ... it can be wrong ... also - what do you have entered for the "Module" setting in the Block Transfers? ... if you're using "one-slot" addressing, then this should be set for "0" ...

stopping and reseating the module is something that I'd hold off on - UNLESS it's really easy to do in your situation ...

I got a chance to take the PLC down, which doesn't happen often. I tried a couple things, re-did the blocks completely, re-seated the card and downloaded. No luck. Swapped cards and every thing works fine. I'm not sure if at some time someone swapped this card because one failed elsewhere or why it failed.

Thanks for the help. Now that I've gone through it in detail and looking for what I did wrong, atleast I know how to do it now.

glad you got it working ...

just one more thought along these same lines ... the 1771-IFE analog INput module is often used along with the 1771-OFE analog OUTput module ... of course, we've only been talking about the OFE module in this thread ...

just a quick note to those who might not already know it ... the 1771-IFE INput modules have a row of jumpers hidden inside the module ... the jumpers determine whether the channels are set up for current or for voltage, etc. ... you have to take the module apart to access these jumpers ... there is NOTHING (no label, etc.) anywhere on the outside of the module telling you this ...

I've seen a few cases where well-intentioned technicians have "swapped" different IFE modules around from one chassis to another during a troubleshooting session ... of course if all of the jumpers aren't set the same in each of the modules, then the results of the "swap" can be very confusing ...

Hi,


Does anyone knows what is the purpose of setting the module (0 or 1) in the BTR or BTW instruction?

Normally I just put 0, when shall 1 be apply?

Thank you.

this "module" entry comes into play whenever the chassis is set up for the two-slot addressing mode ...

specifically, when using two-slot addressing, there could be TWO modules which would have the same RACK address - and the same GROUP address ... the MODULE entry will be 0 for the module on the left - and it will be 1 for the module on the right ...

analogy: the Block Transfer Write is a mailman trying to deliver the mail ... when he gets to the street address he finds that the house is a duplex apartment ... specifically it has an apartment A and it has an apartment B ... so where does the mail go? ... the MODULE designates 0 (for apartment A) or 1 (for apartment B) ...

in most (ALL?) cases where you're not using two-slot addressing, just set the Module entry to 0 and get on with your life ...

hope this helps ...

Ron Beaufort said:

this "module" entry comes into play whenever the chassis is set up for the two-slot addressing mode ...

specifically, when using two-slot addressing, there could be TWO modules which would have the same RACK address - and the same GROUP address ... the MODULE entry will be 0 for the module on the left - and it will be 1 for the module on the right ...

analogy: the Block Transfer Write is a mailman trying to deliver the mail ... when he gets to the street address he finds that the house is a duplex apartment ... specifically it has an apartment A and it has an apartment B ... so where does the mail go? ... the MODULE designates 0 (for apartment A) or 1 (for apartment B) ...

in most (ALL?) cases where you're not using two-slot addressing, just set the Module entry to 0 and get on with your life ...

hope this helps ...

Click to expand...

Hi,

It really helps, thanks a lot for your explaination, very well.

Now my pocket is a bit richer (with knowledge).

Appreciate it.