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6. BIDIRECTIONAL
PROTOCOL
COMMUNICATIONS
MELSEC QnA
6.1.2
Data settina items
The following describes the contents of the data that are designated in the bidirectional mode
control procedure.
Control code
The following table shows the control codes.
Control
Application
Contents
Code
Code
(Hexadecimal)
I
ENQ
I
05H
I
Enauilv
I
Indicates the start of the send data.
I
I
ACK
I
06H
I
Acknowledge
Response to opposite device when data
communications ended normally.
NAK
Response to opposite device when data
Negative Acknowledge
15H
communications ended abnormallv.
Inh
Data length
Two-byte binary data represents the number of bytes
or
number of words of the data area
in a message.
The contents set to QC24 buffer memory address 96H (bidirectional mode word/byte
designation area) determines the data length units.
In this guidebook, data is sent and received in word units.
[Example] The
data length when "AJ71 QC24" and the value
1 0 0
are sent as data is shown
below. (Units: Bytes)
0 5 H
[
AJ71 QC24
10 bytes
b15
'H'
38 b7
-
1Lt
b l b@
iomemory+
0
1
0
1
0
0
0
0
0
0
0
0
0
0
0
0
contents
M
M
I
I
Data area
This is the ordinary 1 -byte data list that is to be sent to the opposite device. Data codes
OOH-FFH are handled.
6 - 3
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