Rockwell Automation Allen-Bradley ControlLogix 1756-MVI Programming Reference Manual page 19

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Application Development Overview
The 1756-MVI API suite allows developers to access the ControlLogix
backplane and serial ports without needing detailed knowledge of the
module's hardware design. The 1756-MVI API Suite consists of three
distinct components:
• the MVI Backplane API
• the CIP Messaging API
• the Serial Port API
The MVI Backplane API and CIP Messaging API provide access to the
ControlBus. The Serial Port API provides access to the serial ports.
The MVI Backplane API is "generic," and is portable among all MVI
form factors from Rockwell Automation and third parties. This
"generic" API performs read/write operations with the form factor's
control processor (PLC) by calling the more specific backplane API
required for that form factor. For example, if running a 1756-MVI, the
generic backplane API calls the CIP API to actually read/write 5550
processor data. If running on third party 1794- form factor, the generic
backplane API calls a SERBUS API to communicate with the Flex
adapter, which in turn sends or receives data to/from a Flex scanner.
The serial port API is portable among all MVI form factors as well.
Since the MVI API uses the CIP API to access the
IMPORTANT
backplane, an application that uses the MVI API
cannot directly access the CIP API (CIPAPI.lib,
CIPAPI.h). Similarly, an application using the CIP API
cannot also use the MVI API. In other words, you
use either the MVI Backplane API or the CIP API to
talk to the 5550, but you cannot use both.
• The CIP API is used if you want to control the
CIP connection between a 5550 processor (or
other originator) and the MVI module.
• The MVI Backplane API is used if you simply
want to read/write data for a single 5550
processor, with no concern about the CIP
connection between the processor and MVI.
Chapter
Publication 1756-RM004B-EN-P - October 2000
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