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Specify whether or not a start code is to be set at the beginning of the data, and
whether or not an end code is to be set at the end. Instead of setting the end
code, it is possible to specify the number of bytes to be received before the re-
ception operation is completed. Both the codes and the number of bytes of data
to be received are set in DM 6649 or DM 6654.
Setting the Start Code, End Code, and Amount of Reception Data
15 0
Bit
End code or number of bytes to be received
For end code: (00 to FF)
For amount of reception data: 2 digits hexadecimal, 00 to FF (00: 256 bytes)
Start code 00 to FF
Defaults: No start code; data reception complete at 256 bytes.
DM 6649:RS-232C port
DM 6654:Peripheral port
8-3-1 Communications Frame Structure
Up to 259 bytes of data (including the start and end codes) can be transferred
with the execution of one TXD(––) or RXD(––) instruction. When there are two or
more start codes, the first start code will be used. Likewise, when there are two
or more end codes, the first end code will be used.
Avoid using commonly occurring characters for the end code. Use CR and LF for
the end code if data transmissions are being cut short because the end code is
occurring within the body of the transmission data.
• No start code and end code
Data (specified number of bytes)
• Start code only
ST Data (specified number of bytes)
• End code only
Data (256 bytes or less) ED
• Both start code and end code
ST Data (257 bytes or less) ED
• CR, LF specified for the end code
Data (258 bytes or less) CR LF
• Both start code (00 to FF) and end code (CR, LF)
ST Data (259 bytes or less) CR LF
8-3-2 Communications Procedure
Brief descriptions of the TXD(––) and RXD(––) are provided below.
Transmission (TXD(––)) Refer to 5-27-2 TRANSMIT – TXD(––) for more details. Always include the spe-
cified port’s Transmit Ready Flag as an execution condition for TXD(––) to en-
sure that this Flag is ON before the transmission can be executed.
1, 2, 3... 1. Check to see that SR 26405 (RS-232C Port Transmit Ready Flag), SR
26413 (Peripheral Port Transmit Ready Flag), SR 28305 (Communications
Board Port A Transmit Ready Flag), or SR 28313 (Communications Board
Port B Transmit Ready Flag) is ON.
RS-232C Communications
Section 8-3