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9. COMMUNICATIONS IN THE NO-PROTOCOL MODE
MELSEC-A
9.
COMMUNICATIONS WITH A COMPUTER IN THE NO-PROTOCOL MODE
Read this chapter when the RS-232C interface with the no-protocol mode
by setting the mode setting switch at the AlSJ71C24 i n position of
"5".
If these interfaces are used with the dedicated protocol and in the bidirec-
tional mode, it is not necessary to read this chapter.
I
9.1
Basics of the No-Protocol Mode
(1)
What no-protocol mode means
In no-protocol communication:
Data written to the no-protocol AlSJ71C24 send area (in buffer
memory) using the TO instruction i n a sequence program is output to
an external device in the same code.
Data received from an external device is read from the no-protocol
AlSJ71C24 receive area (in buffer memory) using the FROM instruc-
tion i n a sequence program.
I
1
buffer memow
1
I
I
In the no-protocol mode, data is not converted to ASCll code i n the
AlSJ71C24. If ASCll code is required, the data must be processed into
ASCll code in the AISCPU.
SCPU
(TO instruction)
Send
(2)
Designating a wordlbyte unit for no-protocol mode communication
(Sequence
Program)
For data communications in the no-protocol mode, a unit of data to be
transmitted may be selected between words and bytes. Default setting
for data unit selection is "word", but selection is possible by writing "1"
or "0" t o address 103H in the buffer memory area.
(Section 7.4.3 gives details about the program to make this setting.)
O O H to FFH
Read
(FROM instruction)
O O H
to
FFH
Send area
- - - -
- - - -
Receive area
O O H to FFH
Receive
O O H
to
FFH
External
device
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