Rockwell Automation 2706-F11J_F11JC_F21J_F21JC DL50 INSTALLATION MANUAL - Manual (Page 58)

Chapter 5
Serial Communications
5–8
Duplex Communications- In this Protocol, the DL50 provides a response to
each command it receives. The response includes data checking bytes
(Checksum) and a handshake byte (ACK/NAK). The DL50 receives message
packets from the master device, transmits data checksum/handshake bytes
back to the master, and uses the message data to display text.
Note: Use Simplex Protocol when the commands are sent from
Allen-Bradley Dataliner DL20 and DL40 message displays, or from other
master devices that do not support duplex communication. The Simplex
Protocol section starts on page 5-2.
The Duplex data packet consists of 7 data fields as shown below:
Control
Byte
Field 1
1 Byte
ASCII Text or
Special Control
Characters
Field 2
1-250 Bytes
Field 3
1 Byte
Slave Address
Field 4
1 Byte
Line Number
Field 5
1 Byte
Carriage Return
Field 6
3 Bytes
Message
Attributes
Field 7
3 Bytes
Checksum
(Dipswitch
Enabled)
Field 1: Control Byte
This field indicates whether the text is to be buffered or displayed when it is
received. The following control characters are used:
Table 5.G
Control Characters in Duplex Protocol
Control Character
Decimal
Value
Function
Ctrl-A 1 Append the characters to buffer. Field 6 is not sent.
Ctrl-B 2 Append characters to buffer then display.
Ctrl-C 3 Clear display line(s). Field 2 is not sent.
Ctrl-D 4 Abandon running message. Reset buffer.
Ctrl-L 12 Initialize DL50 for Bootstrap.
Note:
The Control byte is not optional as in the Simplex protocol.
If the control byte is Ctrl-A (decimal 1), the Message Attributes (field 6) is
not sent because this packet does not cause the DL50 to display text. When
Ctrl-B (decimal 2) is sent with a message attributes field, the message is sent
to the message buffer and then displayed. Text which was previously sent to
the buffer using Ctrl-A message packets is displayed with the message
attributes contained in the Ctrl-B message packet.
A control byte containing Ctrl-D (decimal 4) provides a means of
interrupting the DL50 display. This provides the host with the ability to
display a messages with a higher priority than the message currently being
displayed.
Duplex Protocol