Rockwell Automation 1770-KF3 DH-485 Communication Interface User Manual - Manual (Page 41)

Communicating with the KF3
Chapter 4
4Ć8
03 NAK, Bad LSAP (SRD reply). This link error is returned when
the KF3 receives a NAK, Bad LSAP message from the destination
station in response to an SRD request. This indicates that the
LSAP you are trying to send the SRD request to is invalid for that
destination device.
04 NAK, Unimplemented Function (SRD reply). This link error is
returned when the KF3 receives a NAK, Unimplemented Function
message from the destination station in response to an SRD
request. The most likely cause is invalid data being sent to the
destination device.
05 Invalid or Unsupported Link Type. This link error is returned
if the link type specified does not exist, or the destination of the
message is the KF3 and it does not know how to interpret it. The
KF3 currently recognizes only 01 as a valid link type. Any other
value for the link type will produce this link error.
Link Packet Information
This field contains information specific to the link request. In the case of
an SRD request, this field will contain the Destination Link Service Access
Point (DLSAP) of the SRD.
Command Format, SRD Request
The format of an SRD request command is shown in Figure 4.4:
the CMD byte must be set to 09H
the Link Type byte must be set to 01
the Link Status byte must be set to 00
the Link Packet Information must contain the DLSAP for the slave
station
The format of the data is completely dependent on how the destination
device was implemented. Refer to the destination device’s user manual for
this information.
Figure 4.4
Command Packet Format for an SRD Request
DLE STX DST SRC CMD
09
LINK TYPE
01
LSTS
00
DATA... DLE ETX BCC/CRC DLSAP