Instruction Sheet User guide

Appendix C
Publication 1403-5.1
Serial Communication Protocol Tutorial
The Smart Communication Card supports the DF1 link
layer protocol
For additional information regarding the DF1 link layer
protocol, refer to the
Data Highway/Data Highway
Plus/DH-485 Communication Pr otocol and Command
Set, Allen-Bradley Publication 1770-6.5.16 (November
1991).
T able C.1 contains definitions of single byte codes.
Table C.1 Special Byte Codes
Symbol
Value
SOH 0x01
STX 0x02
ETX 0x03
EOT 0x04
ENQ 0x05
ACK 0x06
DLE 0x10
NAK 0x15
DST Address of destination Powermonitor II
SRC
Address of master (device that is sending this
request)
BCC
8 bit block check character. (For Powermonitor II
used only in poll command where it is equal to the
2’s compliment of the STN value)
CRC
16 bit CRC calculated as described in the CRC16
section below.
STN
Data symbol. Station number of the slave node on
your half-duplex link.
Table C.2 contains definitions of multiple byte codes.
Table C.2 Special Symbol Meanings
Symbol
Type Meaning
DLE SOH
Control
symbol
Sender symbol that indicates the
start of a master message.
DLE STX
Control
symbol
Sender symbol that separates the
multi-drop header from the data.
DLE ETX
BCC/CRC
Control
symbol
Sender symbol that terminates a
message.
DLE ACK
Control
symbol
Response symbol which signals
that a message has been
successfully received.
DLE NAK
Control
symbol
Global link reset command only
issued by the master. Causes the
slaves to cancel all messages that
are ready to transmit to the
master. Typically, the slave
returns the message and an error
code to the originator.
DLE ENQ
Sender symbol, issued only by the
master, that starts a poll
command.
DLE EOT
Control
symbol
Response symbol used by slaves
as a response to a poll when they
have no messages to send. (Only
sent by Powermonitor II if a poll
command is sent that was not
preceded by a read request
command.)
APP DATA Data symbol
Single characters having hex
values 00-0F and 11-FF (i.e.,
00-FF not including 0x10).
Includes data from application
layer including user programs and
common application routines.
DLE DLE Data symbol
Represents the data value or STN
value of 0x10.