Description
A read global data operation reads data from the communications processor of a node on the network that has written global data. A master transaction path is not required.
A read global data operation
can take several cycles if the global data is not currently available
with the nodes called. If global data is available, the operation
is executed in one cycle. To program an MBP_MSTR block
to write global data, use function code 6.
Network Implementation
A read global data operation can be performed only on Modbus Plus networks. The read and write global data operations comprise a Modbus Plus capability known as Peer Cop.
Control Block Usage for Modbus Plus
Register |
Meaning |
|---|---|
CONTROL[1] |
6 = read global data |
CONTROL[2] |
Indicates the error status |
CONTROL[3] |
Number of addresses to be sent from global data memory (comm processor) (1...32) |
CONTROL[4] |
Displays the addresses available in the scanned node. (This register Is automatically updated.) |
CONTROL[5] |
The least significant byte contains the address of the node whose global data is to be read. It can be a value in the range 1 ... 64. If global data is received via a NOM, enter the NOM module slot in the most significant byte of this address. |