Rockwell Automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command - Manual (Page 240)

14–8 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
1775ĆKA. The 1775ĆKA 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 p Indicates the Data Highway node address that is the source of the message. In this example, the reply is
being sent from the 1775ĆKA at node address 011 octal (09 hex).
CMD (command) 4F Indicates the 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 0F hex (unprotected read),
so the CMD byte in the reply message is 4F 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. If the STS byte equals F0 or E0 hex, the exact error is contained in an EXT STS
(extended status) byte. (For more information on STS codes, see page 8-2 .) In our example, the message
is successful (status code 00 hex).
TNS (transaction)
(2 bytes)
02 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. Since our example has three commands, each command must have a different TNS
field.
DATA 228 bytes In our example, the computer reads 228 bytes (114 words) of actual data from the PLCĆ3 data table starting
at B10:0. Each word of data is presented low byte first. The second read command starts at B10:114 and
the third at B10:228 based on the packet offset field.
DLE ETX (2
bytes)
10 03 Indicates the termination of the reply message.
BCC (block check
character)
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.
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 three seconds, it sends a DLE ENQ
to see if reĆtransmission is necessary.