I have used Global Data several times, it is great if you only need to send or receive one word from each processor.
From the help files:
Global Status Word S:99
This is the word reserved to hold the SLC 5/04 (OS401) controller's global status data that is to be transmitted with each DH+ token pass packet over channel 1.
Transmit Control Bit S:34/3
When this bit is set (1), the controller transmits the global status word with every token pass. When this bit is clear (0), the controller passes the token without the global status word. The default state of this bit is 0.
Receive Control Bit S:34/4
When this bit is set (1), the controller places the global status word that it receives from other nodes on the DH+ network into the Global Status word (S:100 through S:163). When this bit is cleared (0), the controller ignores the global status word that it receives from other nodes on the DH+ network. The default state of this bit is 0.
S:100 to S:163 Node
These words comprise the System Status file. This file size is consistent with the number of nodes on the DH+ network and contains the global status words received by these nodes. When received, each DH+ node's global status word is placed in this file and indexed to its node number.
You can use the Global Status File to send a high-speed broadcast to all processors on a network in one token rotation. Using an MSG instruction would require as many MSG instructions and token rotations as there are processors on the network. This is useful for such activities as sending start/stop signals, synchronizing processors, and synchronizing clocks.
RSLogix 500 - Copyright Rockwell Software 2000, 2001, 2002
