Prosoft-technology MVI56E-MCMR Manual do Utilizador descarregar pdf (Página 151)

MVI56E-MCMR ♦ ControlLogix Platform Reference

Modbus Communication Module with Reduced Data Block User Manual

ProSoft Technology, Inc. Page 151 of 225

May 13, 2014

6.3.2 Normal Data Transfer Blocks

Normal data transfer includes the transferring of data received by, or to be

transmitted to, the Modbus drivers and the status data. This data is transferred

through read (Input Image) and write (Output Image) blocks. Refer to Module

Data (page 118) for a description of the data objects used with the blocks and the

ladder logic required. The following topics discuss the structure and function of

each block.

Read Block

Read Blocks transfer data from the module to the ControlLogix processor's

MCMR.DATA.READDATA controller tag array. The following table describes the

structure of the input image.

Read Block from Module to Processor

Word Offset

Description

Length

Write Block ID (1 to 125)

1 to 40

Read Data

Read Block ID (1 to 125)

The Read Block Identification Code (word 41) is used to signal to the

ControlLogix processor that a new block is ready for processing. It also tells the

processor where in the MCMR.DATA.READDATA controller tag array to place the

data contained in the block.

If the value of the code is set to 1, the block contains the 40 words of data from

the module database starting at the address specified in the configuration file

parameter, READ START REGISTER. This data will be put into the ReadData array,

starting at READDATA[0] up to READDATA[39].

Read Block ID 2 would contain the next consecutive 40 words from the module

database to be placed in READDATA[40] up to READDATA[79] and so on, up to

the total amount of data words specified in the configuration parameter, READ

The block also contains the Write Block Identification Code the module expects

to receive from the processor. Under normal data transfer conditions, the ladder

logic should use the Write Block Identification Code to build the appropriate

Output Image data block, unless a special function block is required. The special

function blocks will be discussed in the next section.

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Prosoft-technology MVI56E-MCMR Manual do Utilizador Página 151