17: U
SER
C
OMMUNICATION
I
NSTRUCTIONS
17-16
O
PEN
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C
ONTROLLER
U
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S
M
ANUAL
Designating Constant as Start Delimiter
A start delimiter can be programmed at the first byte in the receive format of a RXD1/RXD2 instruction; the
OpenNet Con-
troller
will recognize the beginning of valid communication, although a RXD1/RXD2 instruction without a start delimiter
can also be executed.
When a constant value is designated at the first byte of source operand S1, the one-byte data serves as a start delimiter to
start the processing of the received data. The valid start delimiter value depends on the data bits selected in Configure >
Function Area Settings > Comm Port > Port 1 or 2 Communication Mode Setting (RS232C) > Communication
Parameters dialog box. When 8 data bits are selected, start delimiters can be 00h through FFh. When 7 data bits are
selected as default, start delimiters can be 00h through 7Fh. Constant values are entered in character or hexadecimal nota-
tion into the source data.
A maximum of five RXD1 and five RXD2 instructions with different start delimiters can be executed at the same time.
When the first byte of the incoming data matches the start delimiter of a RXD1/RXD2 instruction, the received data is pro-
cessed and stored according to the receive format specified in the RXD1/RXD2 instruction. If the first byte of the incom-
ing data does not match the start delimiter of any RXD1/RXD2 instruction that is executed, the
OpenNet Controller
discards the incoming data and waits for the next communication.
While a RXD1/RXD2 instruction without a start delimiter is executed, any incoming data is processed continuously
according to the receive format. Only one RXD1 and one RXD2 instructions without a start delimiter can be executed at a
time. If start inputs to two or more RXD1/RXD2 instructions without a start delimiter are turned on simultaneously, one at
the smallest address is executed and the corresponding completion output is turned on.
Example:
(1) When a RXD1/RXD2 instruction without a start delimiter is executed
(2) When RXD1/RXD2 instructions with start delimiters STX (02h) and ENQ (05h) are executed
****h
D100
When D100 is designated as the first data register
“0”
(30h)
“1”
(31h)
1st
character
“2”
(32h)
“3”
(33h)
Incoming Data
****h
D100+n
****h
D101
The incoming data is divided, converted, and stored to data registers according to the receive format.
****h
D100
RXD Instruction 1
STX
(02h)
“1”
(31h)
“2”
(32h)
“3”
(33h)
Incoming Data
****h
D100+n
****h
D101
The incoming data is divided, converted, and stored to data registers according to the receive format.
Start delimiters are not stored to data registers.
ENQ
(05h)
“A”
(41h)
“B”
(42h)
“C”
(43h)
STX (02h)
When D100 is designated as the first data register
****h
D200
RXD Instruction 2
****h
D200+n
****h
D201
ENQ (05h)
When D200 is designated as the first data register
Compare
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