1 Publication 1764-UM001B-EN-P - April 2002
Appendix
E
Understanding Communication Protocols
Use the information in this appendix to understand the differences in
communication protocols. The following protocols are supported
from the RS-232 communication channel:
• DF1 Full-Duplex
• DF1 Half-Duplex Slave
• DH-485
• Modbus RTU Slave (1764-LSP and 1764-LRP Series B Processors
only)
• ASCII (1764-LSP and 1764-LRP Series B Processors only)
See Chapter 4 for information about required network devices and
accessories.
RS-232 Communication
Interface
The communications port on the MicroLogix 1500 utilizes an RS-232
interface. RS-232 is an Electronics Industries Association (EIA)
standard that specifies the electrical characteristics for serial binary
communication. It provides you with a variety of system configuration
possibilities. (RS-232 defines electrical characteristics; it is not a
protocol.)
One of the biggest benefits of an RS-232 interface is that it lets you
easily integrate telephone and radio modems into your control system.
DF1 Full-Duplex Protocol
DF1 Full-Duplex protocol is an open protocol developed by
Allen-Bradley. It provides a point-to-point connection between two
devices. DF1 Full-Duplex protocol combines data transparency
(American National Standards Institute ANSI - X3.28-1976 specification
subcategory D1) and 2-way simultaneous transmission with
embedded responses (subcategory F1). Refer to DF1 Protocol and
Command Set Reference Manual, publication 1770-6.5.16, for more
information.
DF1 Full-Duplex protocol (also referred to as DF1 point-to-point
protocol) is useful where RS-232 point-to-point communication is
required. DF1 protocol controls message flow, detects and signals
errors, and retries if errors are detected.
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