Rockwell-automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command Uživatelský manuál stáhnout pdf (Strana 240)

14–8 Line Monitor Examples

Publication

17706.5.16 - October 1996

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 1770KF2 put its address in the source (SRC) byte before sending the command message to the

1775KA. The 1775KA 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 1770KF2, 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 1775KA 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 PLC3 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 8bit sum of all data bytes between DLE STX and DLE

ETX.

DLE ACK 10 06 Sent from the computer back to the module (1770KF2) 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 retransmission is necessary.

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Rockwell-automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command Uživatelský manuál Strana 240