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6-1SectionUsing No-protocol Communications
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6-1 Overview
Data can be sent or received without a protocol and without conversion by con-
necting an external device to the RS-232C port and executing the TXD(––) or
RXD(––) instruction from the ladder program. Start and end codes can be at-
tached to the data or the amount of data to be received can be specified.
The communications frame cannot be specified for no-protocol communications
in the way it can be for protocol macros. Retry processing, data conversion, and
procedural branching according to received data are also not possible. No-pro-
tocol communications are thus good for communicating with bar code readers
and other external devices with RS-232C ports that do not required command-
response procedures. Data is sent in one direction only, using TXD(––) to send
data from the port or RXD(––) to read data received on the port.
Note When TXD(––) is executed in No-protocol Mode, data from I/O memory is sent
from the port without conversion. When TXD(––) is executed in Host Link mode
(for slave-initiated communications), the contents of the specified words in I/O
memory is converted to ASCII before being sent.
The specifications of no-protocol communications are given in the following
table.
Item Specification
Messages
(communications
frame)
One of the following.
Data only
Start code + data
Data + end code
Start code + data + end code
Data + CR + LF
Start code + data + CR + LF
Settings are made in the PC Setup: Start code enable, end
code enable, start code, end code, number of receive bytes
(when end code is disabled)
Start code Disabled or 00 to FF Hex
End code Disabled, 00 to FF Hex, or
CR+LF
Number of receive bytes 1 to 256 bytes if transmission
ends in data (data only or start
code + data)
Message
transmissions
TXD(––) in ladder program
Message
receptions
RXD(––) in ladder program
Maximum
message length
256 bytes including start code and end codes (253 bytes
without start/end codes) for either sending or receiving
Data conversion None
Communications
protocol
None
Transmission
delay
0 to 99,990 ms (set in PC Setup in units of 10 ms)
The transmission delay is from the beginning of TXD(––)
execution until execution of the next TXD(––) can be started.
Reception counter The number of bytes received at the port can be counted from
0 to 256 bytes.
No-protocol
Specifications