Rockwell Automation 1775-KA PLC-3 Communication Adapter Module User Manual - Manual (Page 106)

Full-Duplex Protocol
Chapter 10
10Ć2
In general, full–duplex protocol gives higher data throughput, but it can
handle communication between only two peer stations. Half–duplex
protocol provides master–slave polling capability and can handle
communication with as many as 255 slave stations, but it gives lower data
throughput.
This chapter describes the data link layer for full–duplex protocol.
Chapter10 describes the data link layer for half–duplex protocol. Chapter
12 describes the network layer and the application layer for both
protocols.
The full–duplex protocol resembles ANSI X3.28–1976 specification,
combining features of subcategories D1 (data transparency) and F1
(two–way simultaneous transmission with embedded responses).
You can use full–duplex protocol for a point–to–point link or a multidrop
broadband MODEM link that allows two–way simultaneous transmission.
It is more difficult to implement than half–duplex because it requires you
to use interrupts and multi–tasking programming techniques. It is
intended for high– performance applications where you need to get the
highest possible throughput from the available communication medium.
At the 1775–KA module, select the unpolled mode with the LIST function
(chapter 2).
Transmission Codes
Full–duplex protocol is a character oriented protocol that uses the ASCII
control characters extended to eight bits by adding a zero for bit 7. See
ANSI X3.4, CCITT V.3, or ISO 646 for the standard definition of these
characters.
The particular ASCII control characters used are listed below.
Control Character Hexadecimal Code
STX (Start of Text) 02
ETX (End of Text) 03
ENQ (Enquiry) 05
ACK (Acknowledge) 06
DLE (Data Link Escape) 10
Full-Duplex Protocol