Rockwell-automation 1770-KF3 DH-485 Communication Interface User Manua User Manual download pdf (Page 40)

Communicating with the KF3

Chapter 4

47

Slave Packet Formats

To invoke DH-485 link layer services, a special PCCC CMD byte is used

to support the addition of link-specific information to the packet. Setting

the CMD byte = 09 indicates that the packet contains extended link

information.

When the CMD byte = 09, the packet contains a “Link Type” field (one

byte), a “Link Status” field (one byte), and information specific to the

link-type command being sent.

Figure 4.3 shows the SRD request packet format.

Figure 4.3

The

SRD Request Packet Format

DLE STX DST SRC CMD

LINK

TYPE

LSTS LINK PACKET

INFORMATION

DATA... DLE ETX BCC/CRC

Link Type (LTYP)

This one-byte field defines the Link Type as follows:

1 – SRD Link Request

2-255 – Reserved for future expansion

Link STS (LSTS)

This one-byte field indicates the Link Status of the SRD request. It is used

on replies to SRD requests only. When sending an SRD command, this

field should be set to zero.

00 Success. The message was successfully sent to the destination

device. Note that some slaves will return data with the success

code (ACK with Data).

01 NAK, No Memory at Destination (SRD reply). This link error

is returned when the KF3 receives a NAK, No Memory message

from the destination station in response to an SRD request.

02 NAK, Undeliverable Message (SRD reply). This link error

is returned if the 1770-KF3 was unable to send the SRD to the

destination station (as may occur when the destination does not

exist on the network).

1 2 ... 35 36 37 38 39 40 41 42 43 44 45 ... 58 59

No comments

Rockwell-automation 1770-KF3 DH-485 Communication Interface User Manua User Manual Page 40