User Manual

A–B

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 (<ESC>=!) 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