Chapter Objectives; Understanding Block Transfer - Allen-Bradley 1203 Series User Manual

Chapter Objectives

Understanding Block Transfer

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Using Block Transfer Messages
Chapter 5 provides information about Block Transfer messages. In
this chapter, you will read about the following:
• General information on block transfers.
• The Remote I/O status word.
• Data storage.
• Example ladder logic programs using Block Transfer messages.
ATTENTION: The sample programs and block transfer
!
examples shown in this manual are intended solely for pur-
poses of example. Since there are many variables and re-
quirements associated with any particular installation,
Rockwell Automation does not assume responsibility or li-
ability (to include intellectual property liability) for actual
use based upon the examples shown in this publication.
ATTENTION: Hazard of equipment damage exists. If
!
block transfer messages are programmed to frequently
write parameter data, the EEPROM (Non-Volatile Storage)
will quickly exceed its life cycle and cause the product to
malfunction. Do not create a program that frequently uses
block transfer messages to write parameter data to a
product. Datalinks do not write to the EEPROM and should
be used for frequently changed parameters.
Discrete transfer is the method used by a controller to transfer data to
and from the module during every rack scan. The module transfers
this data to and from the SCANport product.
Block transfer is the method used by a controller to transfer data that
does not require continuous updates. To perform this function, the
module provides a status word to the controller during the normal
discrete transfer scan. This status word occupies the first module
group (word) in the I/O image table for the designated rack
(communications module). The status word is then used by the ladder
program to control the controller Block Transfer Write (BTW) and
Block Transfer Read (BTR) functions.
Important: The Remote I/O communications module does not scale
or manipulate data that is transferred between the
controller and SCANport product. The data in the
controller must be converted to device units before being
sent to the SCANport product.
5
Chapter