Rockwell Automation 6001-F2E AB STANDARD DRIVER SFTW - Manual (Page 40)

Specifying Message Packet Commands
with Send_StdDrv()
Appendix B
B-3
Communicating with a Slave-only Device
Figure B.2 shows the message packet format you use to communicate
with a slave-only DH-485 device.
Important: Shaded blocks indicate packet fields that may or may not be
included in your message packet, depending on the command.
Figure B.2
Message Packet Format for Communicating with a Slave-only Device
LEN TYP DST SRC CMD STS TNS FNC ADDR SIZE IMMED. 1 DATA TNS
Table B.B shows the message packet fields in Figure B.2.
Table B.B
Communicating with a Slave-only Device
This Packet Field Is the
LEN length of the message packet (including LEN)
TYP type code identifying this format
(this is always a 5)
IMMEDIATE BLOCK immediate block in the destination device
1 local link message
(this is always a 1)
DST DH-485 destination address for this packet
SRC DH-485 address of the device sending the packet
CMD command byte
STS message packet status
TNS transaction number (2 bytes)
FNC byte used with CMD. If used, it defines the specific function
under the command type
ADDR two-byte field that contains the address of a memory
location in the command executor where the command is to
begin executing.
SIZE byte that specifies the number of data bytes to be
transferred by a message
DATA data sent as part of a message command
The next section describes the packet fields for both applications.