1794 id2

[roxusa]

I see no threads about the 1794 ID2 incremental encoder module.
I have used Flex logix before but have not done Block transfers to any of the special modules. Does anyone have any programing examples on setting up one.I have the user manual but could use some pointers. I am looking to add several of these to a new project. I have used the 1746 HSCE before but would like to keep the encoders remote at each station. Thanks

 

[Ken Roach]

Are you literally using a FlexLogix controller, or are you using a network adapter with a ControlLogix family controller ?

A quick search of the RA Knowledgebase turns up a handful of related application notes, including a good comparison between the various FLEX platform high speed modules:

https://rockwellautomation.custhelp.com/app/answers/detail/a_id/40183

What sort of application are you doing ? Is the input an encoder, or a pulse generator, or something else ?

 

[roxusa]

I have multiple machines running on SLC 500 with a SN communicating between the ASB
units. These are large machines on tracks that open up for setup and cleaning. The RIO has worked well for 14 years. I realize there are numerous newer options available. But without changing the entire machine I would like to add a few encoders for either auto positioning or at the very least a position readout for manual move. I have room to ad the ID2 modules to each of the racks.

 

[Ken Roach]

Ok, so you have SLC-500 controllers with 1747-SN Series B RIO scanners, and you have 1794-ASB adapters for FLEX I/O at some of your stations.

So you are going to have to literally use Block Transfers to get data in and out of the 1794-ID2 modules.

Your project really starts with learning about Block Transfers in the SLC-500 platform, which is a complicated topic itself.

The first thing I would do is perform a survey of the operating system and firmware revision of all of your SLC-500 controllers. If they've been running for 14+ years, they're very likely too old to support the BTW and BTR instructions so you'll have to get out the old-fashioned 1747-SN/B user manual and start with the basic examples of formatting Block Transfer command and reply blocks.

I recommend starting with the Knowledgebase articles 15175 and 31770:

https://rockwellautomation.custhelp.com/app/answers/detail/a_id/15175

https://rockwellautomation.custhelp.com/app/answers/detail/a_id/31770/related/1

 

[roxusa]

Thanks, The SLC's I am using are 532E and support BTR & BTW. I have used both and have them communicating with the Panel Views. This is just for the numeric readouts and data entry. I was not sure if communicating with a specialty module worked the same.

 

[Ken Roach]

The BTR and BTW instructions make programming advanced RIO network applications an order of magnitude easier. I'm glad you will have them.

The Knowledgebase article 40183 says the 1794-ID2 takes a Block Transfer Write of 7 Words in length, and a Block Transfer Read of 8 Words in length.

That conflicts with the I/O image shown in the 1794-ID2 User Manual in Chapter 4 for RIO, which shows just 5 words for the BTW.

I suspect the Knowledgebase article is incorrect and confused the size with the two-extra-words size for DeviceNet.

I don't know if you'll find an exact example of using BTR/BTW instructions with an SLC-500 and the 1794-ID2.

I think the module is reasonably straightforward, so I'd just give it a shot armed with Chapter 4 of the User Manual.

 

[roxusa]

does that mean the I/O image in the scanner would be a full rack for the one module.

 

[Ken Roach]

Discrete I/O memory vs. Block Transfers

I'm going to simplify a little. In the usual "Standard" addressing mode of the 1794-ASB adapter, each FLEX module gets 1 Word of Input data and 1 Word of Output data that is automatically scanned by the RIO scanner and put into the ordinary I/O memory of the SLC-500 controller.

That makes an assembly of 8 FLEX modules = one "Logical Rack" of RIO memory.

There are other methods for expanding the number of words per physical module, but none of them will get you to the size that a Block Transfer can access.

The block transfer actually takes over the use of the low byte of that one Input and one Output word, so most devices that use Block Transfer do not also use the discrete I/O memory.

The 1794-ID2 does not use any of the discrete I/O memory, but instead relies entirely on the Block Transfers.