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9. COMMUNICATIONS IN THE NO-PROTOCOL MODE
MELSEC-A
If these interfaces are used with the dedicated protocol and in the bidirec-
tional mode, it is not necessary to read this chapter.
9.
COMMUNICATIONS WITH A COMPUTER IN THE NO-PROTOCOL MODE
9.1
Basics of the No-Protocol Mode
D
(1) What no-protocol mode means
Read this chapter when the RS-422 and RS-232C interface with the dedi-
cated protocol and in the no-protocol mode by setting the mode setting
switch at the AJ71C24 i n any position of "1" to
"8".
In no-protocol communication:
Data written to the no-protocol AJ71 C24 send area (in buffer memory)
using the
TO
instruction in 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
AJ71C24 receive area (in buffer memory) using the FROM instruction
in a sequence program.
W,i,n
I
buffer memory
I
I
.....
"
PC;
CPU
,.
3 instruction)
Send
OOH to FFH
External
(Sequence
WH to FFH
device
Program)
Read
- - - - - -
In the no-protocol mode, data is not converted to ASCll code in the
AJ71 C24. If ASCll code is required, the data must be processed into ASCII
code in the PC CPU.
(FROM instruction)
WH
to
FFH
(2)
Designating a wordlbyte unit for no-protocol mode communication
Receive
Receive area
OOH to
FFH
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" to address 103H in the buffer memory area.
(Section 7.4.3 gives details about the program to make this setting.)
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