Rockwell Automation 2755-DM9, -DM9E High Speed Decoder - Manual (Page 113)

A–B
8 Chapter
8–1
Host Commands Using the RS-485 Interface
In this chapter, we tell you how to send host commands to the decoder when
you are using the RS-485 interface. We also provide the format of the
decoder’s response.
When you use the RS-485 communications interface, you have four protocol
options. These options are selected as part of the decoder’s configuration.
Refer to HOST PROTOCOL field description (Chapter 4). Your options are:
•
RS-485 PCCC-1 Protocol with Write Replies
•
RS-485 PCCC-2 Protocol without Write Replies
•
RS-485 ASCII-1 Protocol with Responses
•
RS-485 ASCII-2 Protocol without Responses
Note: Refer to Appendix E for a protocol selection chart which lists all of the
protocol options.
The DM9 supports the following Link Service Access Points (LSAPs):
LSAP FUNCTION
0 Diagnostic Status
1 PCCC Application Services
128 PCCC or ASCII Application Services
129 Link Reset- Immediate Block
If you select RS-485 ASCII, the decoder will accept commands in the form
of ASCII strings and you can use the commands described in Chapter 7.
However, the start command sequence (=!) is unnecessary and cannot
be used with RS-485 ASCII. The remainder of this chapter describes the
Programmable Controller Communication Commands.
Note: If you select RS-485 ASCII-2 (without response codes), you will keep
the data traffic on the RS-485 link to a minimum. Response codes are
usually unnecessary since the link layer of an Allen-Bradley RS-485 network
insures that a command is properly received.
Chapter Objectives
RS-485 Command Protocols
RS-485 ASII Command Protocol