User manual

Transferring Data Using Communication Blocks
170
33002479 06 07/2008
Read Global Data
Description A read global data operation reads data from the communications processor of a
node on the network that has written global data (see Write Global Data, p. 169). 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 (see Operational Function Codes, p. 151).
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.