Allen-Bradley 1779-KFMR User Manual page 98

Chapter 7
Introduction to Message Sets
7 2
Time Critical Message Set
You can send and receive time-critical messages between your host device
and the 1779-KFM interface only if you select the Native mode.
Time-critical messages can read from and write to host devices at remote
stations. Also, time-critical messages can read immediate-access blocks
stored in interfaces of programmable controller stations. Any message
that is not in the time-critical message set is a supervisory message. If
two messages are waiting to be transmitted when a node gets the token on
the Data Highway II link, a time-critical message is given priority over
supervisory messages at that node. Therefore, the predictable response
time for time-critical messages is shorter than that for supervisory
messages; but, you are limited to transferring 21 words maximum using a
read immediate-access block command and limited to transferring less
using other time-critical commands.
The time-critical message set is described in Chapter 9.
Remote Command Control Message Set
You can send and receive remote command block messages between your
host device and the 1779-KFM interface only if you select the Native
mode.
A remote command is a command you send to be stored at a remote
programmable controller station. You can store up to 256 remote
commands in each programmable controller interface. You envelope a
remote command with a store remote command message to send it to a
remote station for storage. Once you store a remote command at a remote
station, you can send one command to the remote station to have it initiate
up to 122 of the stored remote commands as if the remote station had
originated them. This gives the host computer connected to the
1779-KFM interface the ability to control communication between
programmable controllers.
The remote command block message set is described in Chapter 10.