Installation guide

Estimating Network Performance

890 USE 100 00

For example, in a data Read or Write operation, the Control Block

layout is as follows:

4x Operation Type 1 = Write

2 = Read

4x + 1 Storage for Returned Error Status Code (if an error occurs)

x + 2 Data Block Length 4

4x + 3 Start of the Data Area in the Destination Device

4x + 4 Modbus Plus Routing Path 1

4x + 5 Modbus Plus Routing Path 2

4x + 6 Modbus Plus Routing Path 3

4x + 7 Modbus Plus Routing Path 4

4x + 8 Modbus Plus Routing Path 5

The Control Block register at 4x + 2 specifies the length of the data

area for the read or write operation. For example, if this register

contains a value of 32 decimal, that many registers of data will be

transferred in the operation.

The Control Block register at 4x + 3 defines the starting location of the

data buffer in the destination device. Its contents are an offset value

(not an absolute address). For example, a value of 1 specifies reference

40001 in a programmable controller. The offset can be incremented in

successive MSTR operations to move large areas of data.

Data Area Start is a 4x reference that is the starting register in a block

of upto100 consecutive registers that will be used as the local data

buffer in the Read or Write. If the operation is a Read, the incoming

data from the destination device will be stored into this buffer. For a

Write, the buffer contents will be sent to the destination device.

Data Area Size is an absolute value in the range 1 ... 100 decimal. It

specifies the maximum quantity of registers to be allocated for the

MSTR function’s data area.