Rockwell Automation 1770-KF2 Data Highway or Highway Plus Interface Module User Manual User Manual
Page 109
Message Packet Formats
Chapter 5
5-30
Only a computer can initiate privileged commands. Their primary use is
for uploading and downloading PLC-3 memory.
Only a computer or another PLC-3 station can initiate the non-privileged
PLC-3 commands listed above. Their primary use is for transferring data
between two PLC-3 files. Those files may be located in the same PLC-3
processor in two different PLC-3s.
In addition to the message packet fields already described for the basic
command set (see “Message Packets”), PLC-3 messages may also contain
the following fields:
1.
ASCII SYMBOL — Contains the ASCII codes for the characters
in a PLC-3 symbolic address. Chapter 6 gives more information on
the format of symbolic addresses.
2.
PACKET OFFSET — Contains the word offset between the
DATA field of the current message packet and the DATA field of the
first packet in the transaction. This offset value appears only in
command messages for file transfers, where the complete transaction
might require more than one command or reply message packet. The
value of PACKET OFFSET is zero for the first packet in a
transaction.
3.
PLC-3 LOGICAL ADDRESS — Contains the logical address of a
PLC-3 file or word. Chapter 6 gives more details about the contents
of the address field.
4.
PLC-3 PHYSICAL ADDRESS — Contains the physical address
of a PLC-3 word. Chapter 6 gives more details about the contents of
this address field.
5.
TOTAL TRANS — Contains the total number of data words
transferred by the current transaction. This is the total number of
PLC-3 words to be transferred in the DATA fields of all message
packets in the current transaction. TOTAL TRANS appears only in
command messages for file transfers, where the transaction might
take more than one message packet to complete.
6.
W/F — Is the word/file symbolic address flag. This one-byte flag
specifies whether the symbolic address field following it represents a
word address or a file address. The value of W/F is zero if the
symbol represents a word address and non-zero if the symbol
represents a file address.