Installation guide

Estimating Network Performance
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3.21.2 Using Peer-to-Peer Communication Techniques
Use peer-to-peer passing of data where applicable, rather than
master-slave polling. For example, in a master-slave process you can
have a user interface device perform polling of your process control
devices to determine if status updates are necessary. Using a
peer-to-peer technique, you can have each process device initiate
messages to the user interface device as events happen in the process.
This reduces the total quantity of transactions on the network,
improving network performance.
Destination devices must be able to sense the presence of new data and
handle it before more data is received. One way to do this is to have
each destination device maintain a write status register for each other
device that can originate data to that application. When new data is
sent, this status register is written into in addition to the data registers
that are written. A new data ready sentinel bit can be set by the write
operation, and can be reset by the local application when the data is
extracted and used. Other bits in the status register can indicate the
data block length, target task, and other information. Additional
registers can be used for this purpose if required.
The destination device’s software can handle missed events internally
on a timeout basis, rather than by polling, and still manage orderly
shutdowns. Plan your application from the start to use effective
techniques for throughput.
3.21.3 Using the Global Database
You can broadcast up to 32 registers using the network’s global
database, with up to 64 nodes receiving this data during the current
token pass. This can be most effective in data acquisition and alarm
handling, in which many devices can react quickly to a single
transmission of data.
The MSTR Write Global Database function executes upon release of the
token by the initiating node. The MSTR Read Global Database
function executes during the scan of each receiving node, making the
data available immediately to the node’s application.