972
Serial Communications Instructions Section 3-24
Example In this example, IOWR(223) is used to write data.
3-24 Serial Communications Instructions
This section describes instructions used for serial communications.
3-24-1 Serial Communications
There are two types of serial communications instruction. The TXD(236),
RXD(235), TXDU(256), and RXDU(255) instructions send and receive data in
no-protocol (custom) communications with an external device. PMCR(260)
sends and receives data using user-defined protocols with an external device.
The difference is shown in the following tables.
Note 1. The TXD(236) and RXD(235) instructions transfer data only through the
CPU Unit’s built-in serial port or a serial port on a Serial Communications
Board (Ver. 1.2 or later).
2. The TXDU(256) and RXDU(255) instructions transfer data only through a
Serial Communications Unit (Ver. 1.2 or later).
D
D+1 D
CPU Unit
When CIO 000000 is turned ON, the 10 words in D00100 to
D00109 are written to the Special I/O Unit.
Number of words
to transfer: 10
Unit number: 3
The control code (C) varies depending on the Special I/O Unit.
Special I/O Unit (Unit #3)
10 words
Instruction Mnemonic Function code Page
PROTOCOL MACRO PMCR 260 974
TRANSMIT TXD 236 983
RECEIVE RXD 235 993
TRANSMIT VIA SERIAL COMMU-
NICATIONS UNIT
TXDU 256 1005
RECEIVE VIA SERIAL COMMU-
NICATIONS UNIT
RXDU 255 1013
CHANGE SERIAL PORT SETUP STUP 237 1021
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