Rockwell-automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command Uživatelský manuál stáhnout pdf (Strana 236)

14–4 Line Monitor Examples

Publication

17706.5.16 - October 1996

Command

Field Value Function

DLE STX (2 bytes) 10 02 Indicates the start of a message

DST (destination) 09 Indicates the remote node address that the computer is communicating to. 09 hex equals 011 octal,

the address of the 1771KA2.

SRC (source) 00 Indicates the Data Highway node address that is the source of the message. In this example, the computer

uses an SRC byte of 00 (hex). The asynchronous interface (1770KF2) automatically inserts the correct

SRC value before sending the message across Data Highway to the 1771KA2.

CMD (command) 01 Indicates the specific type of command. In this example, the CMD byte has the value 01 (hex) which

indicates an unprotected read of the PLC2/30 data table.

STS 00 Indicates the status of the message. A command message should always set this field to 00 (hex).

TNS (transaction)

(2 bytes)

01 00 Indicates a specific transaction value for each message. The TNS value increments for each message

packet. This value makes each message uniquely different, which helps you check for duplicate message

packets.

ADDR (address)

(2 bytes)

11 00 Specifies the PLC2 data table address where the unprotected read starts. The combination of these two

bytes points to a byte address. Since the PLC2 works in word (2 byte) increments, the address should

specify an even number of bytes. The address must be transferred low byte first. In our example,

the address 11 00 (hex, low byte first) equals 000 022 octal byte address or 000 011 octal word address.

SIZE 02 Specifies how many bytes of PLC2 data table information you read in this transaction.

DLE ETX (2 bytes) 10 03 Indicates the termination of the message.

BCC (block check

character)

E2 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. (For more information on BCC and CRC error checking, see page 5-4 .)

DLE ACK 10 06 Sent from the module (1770KF2) back to the computer to indicate that the module 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) instead of the DLE ACK (hex).

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Rockwell-automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command Uživatelský manuál Strana 236