BTR instruction max block length

[BeepBob]

Hello all,

I see that the Block Transfer Read instruction can read a max length of 64 words

I have a Hilscher gateway to map DeviceNet Slave to ModbusTCP

Each input takes up 1 register/word

I have 60 devices that needs 4 words each. So that is 240 words.


Is there a way to read all the data beyond 64 words from a devicenet node?

 

[alan_505]

Multiple BTR's ?

 

[BeepBob]

Multiple BTR's ?

I was thinking that, but in the scanner, I can only map up to 64 words, so i guess that answers my question, the scanner can only read/write 64 words per node?

 

[alan_505]

Then it sounds like you will need multiple scanners.

 

[Ken Roach]

Is there a PLC-5 involved in this ? I'm not sure where Block Transfers are coming from.

In general, a DeviceNet frame can transport 8 bytes of data, and the "fragmentation protocol" and can use multiple frames to transport larger amounts of data. There's no protocol limit but there are certainly device and practical limits to how large an I/O connection can be.

This system sounds familiar; I think I advised against using DeviceNet at all, but there were reasons.

 

[BeepBob]

Is there a PLC-5 involved in this ? I'm not sure where Block Transfers are coming from.

In general, a DeviceNet frame can transport 8 bytes of data, and the "fragmentation protocol" and can use multiple frames to transport larger amounts of data. There's no protocol limit but there are certainly device and practical limits to how large an I/O connection can be.

This system sounds familiar; I think I advised against using DeviceNet at all, but there were reasons.

Yes Hello Ken,

It is a PLC5 as the PLC. It just has to live like this awhile longer before our more modern PLCs gets in.

The thing is, I am using one Hilscher gateway to pull together many modbus TCP devices and then translating it to DeviceNet for the PLC5.

I am running into 200 ish words of data per Hilscher gateway, because the Emerson RSTI-OM module somehow can't splice 4 inputs worth of data onto one register (even though the manual say it can, most likely its my fault somewhere).

The maximum input mapping the 1771-DeviceNet Scanner can do is 64 words per channel...I got 2 cards, so 4 channels, but I wish I can just do 1 channel 1 card and get rid of 3 DeviceNet runs. But it seems I may have to use both channels on both cards and 4 Hilscher gateway.....

The attached screen shot shows that it takes 9 WORDS just to collect 4 inputs and 3 outputs from one RSTI-OM..although I think I can cut 2 WORDS out as those two words does nothing

 

[BeepBob]

So I read in the 1771-SDN manual

"The scanner module can update a maximum of 357 input words by internally linking together six different sized block transfers. "

Does that mean I can do 3-4 BTR instruction to get all of my required data into the PLC5?

 

[BeepBob]

I think I have my own answer. I can just select enough block transfers to accommodate my input data need. Then create BTRs with the respective block transfer size (length) to target those blocks.