Configuration Manual Owner manual

Publication 1757-PM002A-EN-E - June 2006

3-6 Basic Function Blocks

Relationship of Output Function Blocks to the Transducer

Initial Configuration: Virtual

Communication

Relationships

Virtual Communication Relationships (VCRs) are communication links on an

H1 network. A total of 128 VCR’s are possible within the linking device, and

these VCRs are restricted to 32 per H1 channel. This is further restricted to 16

VCRs going to the Control Logix processor from H1 devices and publishers,

and 16 VCRs coming from the Control Logix processor to H1 devices and

subscribers.

These restrictions limit the number of inputs and outputs within an H1 line.

However, there is no restriction on the type of signals. They can all be analog,

all discrete, or a mix of the two. The only restriction is the 16 publisher and 16

subscriber limits.

If the VCR limit is exceeded, a download will still be permitted, although when

the download reaches the 17

VCR, a “download failure” will occur. The first

16 VCR’s will still be in place, but the 17

will not exist.

VCR Classes

The Foundation Fieldbus specification Fieldbus Access Sublayer (FF-875-1.4)

defines three classes of Virtual Communication Relationships that are possible

for communications with an H1 field device. These classes are:

• BNU: Buffered Network-Scheduled Unidirectional

• QUU: Queued User-triggered Unidirectional

Output

Transducer

Block

Manufacturer

Specific

I/O

Subsyste

Channel

ameters

Output Snap

of Transducer

Block

Inputs

Block

Algorithm