User manual

set ia
Chapter 2 Command Descriptions 123
priority={high|medium|low}
Normally messages are processed in a fair round-robin scheme. This
becomes unfair when one master acts as many – for example opening
16 TCP sockets to talk to 16 slaves contrasted to a second master
using a single TCP socket to talk to 16 slaves. In this situation, the
device assumes it has 17 masters and in effect the first master will
have 16 requests answered for every one the second master
succeeds in getting answered. This option can be used to adjust the
handling of serial master requests. For example, set the serial master
to High and the network masters to medium. The effectiveness of this
option depends on the protocol behavior – so while some Modbus
systems will find it useful, it has no effect on most Rockwell protocols.
high
A high-priority master can get up to 50 percent of the bandwidth –
of course you cannot have too many high-priority masters. All high-
priority masters with queued messages get one message serviced
before any low or medium priority masters get any service.
medium
If a high-priority master has queued messages, then one medium-
priority master gets one message serviced before all the high-
priority masters are offered service again. If only medium-priority
masters exist (which is the default setting), then all masters are
serviced in a round-robin manner.
low
Low-priority masters only get service when no High- or Medium-
priority master has messages to service.
The default is “medium.”