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Serial Communications Instructions Section 3-24
The following diagram shows the order in which data is sent and the contents
of the send frame for various start and end code settings.
Flags
Precautions TXDU(256) can be used only for a Serial Communications Unit’s serial port
that has been set to no-protocol mode.
The following send-message frame formats can be set in the allocated DM
Setup Area.
• Start code: None or 00 to FF hex.
• End code: None, CR+LF, or 00 to FF hex.
The data will be sent with any combination of start and/or end codes specified
in the allocated DM Setup Area. If start and end codes are specified, the
codes will be added to the send data (N). In this case, the maximum number
of bytes that can be specified for N is 256 bytes.
Data is sent in the order specified in C.
Nothing will be sent if 0 is specified for N.
If RS signal control is specified in C, bit 15 of S will be used as the RS signal.
1
3
5
2
4
6
CR LF
CR+LF End Code
Only End Code
Data
Data
Data
Data
Data
Data
N bytes of data is sent in the following order when
sending the most significant bytes first is specified:
1, 2, 3, 4, 5, 6
No Start or End Code
N send bytes: 256 max.
Only Start Code
Send bytes after ST:
256 max.
Send bytes before ED:
256 max.
Start and End Code
Send bytes between
ST and ED: 256 max.
Send bytes before
CR+LF: 256 max.
Send bytes between ST
and CR+LF: 256 max.
Start and CR+LF End Code
Serial port on Serial Communications Unit
Data sent.
15
8 7
0
Name Label Operation
Error Flag ER ON if all of the logical ports are being used or the Com-
munications Port Enabled Flag for the specified logical
port is OFF when the instruction is executed.
ON if the value of C is not within range.
ON if the value for N is not between 0000 and 0100 hex.
OFF in all other cases.
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