Configuration Manual Owner manual

Publication 1757-PM002A-EN-E - June 2006

3-8 Basic Function Blocks

The user would be under the impression that there are 64 publishers and 64

subscribers available. This is both correct and incorrect at the same time. The

user can correctly use the total quantity, but it must be evenly distributed

among the four H1 channels that the linking device uses. In other words, each

channel owns 16 publishers and 16 subscribers. The 16 publishers and 16

subscribers are dedicated to each channel; they cannot be shared if not used by

one particular channel.

BNU Class

The BNU class is defined as scheduled. It occurs on a synchronous basis

within the macrocycle schedule. During the scheduled portion of Foundation

Fieldbus communications, when the devices receive the Compel Data token,

this is the class of communication that occurs. The BNU VCR is part of the

function block strategy that transfers data from one function block to another.

This class can be further defined as the link between function blocks. More

specifically, the BNU VCR is the unique link between function blocks in

different devices. Links between function blocks within a device do not use a

BNU VCR. Also, links that are used multiple times, or fanned out, between the

same devices are not considered unique.

The BNU VCR is also defined as to whether it is a publisher or a subscriber.

Therefore, the use of a VCR relative to a device is very important. The

connection of the link from one function block to another in a different device

will be counted based on its point of origin. The originating device will

consume a publisher VCR, whereas the receiving device will consume a

subscriber VCR.

Examples of the BNU VCR counting are provided to emphasize the above

statements:

1. Linking Device: 1 Subscriber

Device 1: 1 Publisher

MaximumNumberOfServerVcrs = 5

MaximumNumberOfSourceVcrs = 8

MaximumNumberOfSinkVcrs = 0

MaximumNumberOfPublisherVcrs = 64

MaximumNumberOfSubscriberVcr

= 64