Prosoft-technology MVI69-ADM Manual de usuario descargar pdf (Pagina 45)

MVI-ADM ♦ 'C' Programmable Understanding the MVI-ADM API

'C' Programmable Application Development Module Developer's Guide

ProSoft Technology, Inc. Page 45 of 342

February 20, 2013

Normal Data Transfer

Normal data transfer includes the paging of the user data found in the module’s

internal database in registers 0 to 4999 and the status data. These data are

transferred through read (input image) and write (output image) blocks. The

structure and function of each block is discussed in the following topics.

Block Request from the Processor to the Module

These blocks of data transfer information from the PLC processor to the module.

The following table describes the structure of the output image.

Offset

Description

Length

Write Block ID

1 to 60

Write Data

61 to 63

Spare

The Write Block ID is an index value used to determine the location in the

module’s database where the data will be placed. Each transfer can move up to

60 words (block offsets 1 to 60) of data.

Block Response from the Module to the Processor

These blocks of data transfer information from the module to the PLC processor.

The following table describes the structure of the input image.

Offset

Description

Length

Read Block ID

Write Block ID

2 to 61

Read Data

62 to 63

Spare

The Read Block ID is an index value used to determine the location of where the

data will be placed in the PLC processor user data table. Each transfer can move

up to 60 words (block offsets 2 to 61) of data.

The Write Block ID associated with the block requests data from the PLC

processor. Under normal program operation, the module sequentially sends read

blocks and requests write blocks. For example, if the application uses three read

and two write blocks, the sequence will be as follows:

R1W1R2W2R3W1R1W2R2W1R3W2R1W1

This sequence will continue until interrupted by other write block numbers sent by

the controller or by a command request from a node on the foreign network or

operator control through the module’s Configuration/Debug port.

If the ladder logic does not send a BTW instruction to the module quickly enough,

it is possible for the MVI71-ADM module to send a new BTR instruction

requesting the same write block ID.

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