Rockwell Automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command - Manual (Page 237)

14–5 Line Monitor Examples
Publication 1770Ć6.5.16 - October 1996
Reply
Field
Value Function
DLE STX (2 bytes) 10 02 Indicates the start of the reply message
DST (destination) 0A Indicates the node address that the reply is being sent back to. In our example command message,
the 1770ĆKF2 put its address in the source (SRC) byte before sending the command message to the
1771ĆKA2. The 1771ĆKA2 takes the source byte from the command message and makes it the destination
byte of the reply message. In our example, the reply message is sent back to the 1770ĆKF2, node address
012 octal (0A hex).
SRC (source) 09 Indicates the Data Highway node address that is the source of the message. In this example, the reply is
being sent from the 1771ĆKA2 at node address 011 octal (09 hex).
CMD (command) 41 Indicates the specific type of command. In a reply packet, 40 hex is added to the CMD byte to indicate that
the packet is a reply. In this example, the CMD byte in the command message was 01 hex (unprotected
read), so the CMD byte in the reply message is 41 hex.
STS (status) 00 Indicates the status of the message. If there is a problem with the message or the network, a status code
appears in this byte. In our example, the message is successful (status code 00 hex). (For a list of status
codes, see Chapter 8, Message Packet Status Codes (STS, EXT STS).")
TNS (transaction)
(2 bytes)
01 00 Indicates a specific transaction value for each message. The TNS value for the reply message is the same
as the TNS value for the command message. This allows the computer to keep track of commands and their
associated replies.
DATA FF FF In our example, the computer reads two actual bytes of data from the PLCĆ2/30 data table (octal word 011).
These bytes of data are FF FF hex (1111 1111 1111 1111 binary). This indicates that all 16 bits at octal word
011 are set on.
DLE ETX (2
bytes)
10 03 Indicates the termination of the reply message.
BCC (block check
character)
AD Used to check the accuracy of the message transmission. You can optionally use CRC bytes here.
The BCC value must equal the 2's compliment of the 8Ćbit sum of all data bytes between DLE STX and DLE
ETX. (For more information on BCC and CRC error checking, see page 5-4 .)
DLE ACK 10 06 Sent from the computer back to the module (1770ĆKF2) to indicate that the computer successfully received
the message. If the BCC value calculated by the module does not match the BCC value in the message
packet, the module sends a DLE NAK (10 15 hex) instead of the DLE ACK (hex). If the module does not
receive a DLE ACK or DLE NAK from the computer within approximately one second (1771ĆKE, ĆKF, ĆKG
only), it sends a DLE ENQ to see if reĆtransmission is necessary.