Mitsubishi Electric MELSEC-A Manual Book page 83

6. COMMUNlCATlONS IN THE BIDIRECTIONAL MODE
MELSEC-A
6.3.2
Data settings
This section describes the elements of data specified in the control procedure
for the bidirectional mode.
(1)
Control codes
The following table shows control codes:
%
Hexadecimal
I
NAK
I
15H
Description
1
Function
~~~ ~~~~ ~
Enquiry
Code indicating
the start
of send
data.
ICode to be sent to the
Acknowledge
I
communicating device on normal
termination of data
Icommuntcattons.
ICode to be sent to the
Negative Acknowledge
I
communicating device on
abnormal termination of data
Icommunications.
'
(2) Data length
The number of bytes or words of the data area in the text is expressed
in 2- byte binary data.
The data length unit (wordshytes) depends on the contents of the buffer
memory address 103H (bidirectional word/byte setting area) in the
AJ71 UC24.
This guidebook describes data transmission and reception in word units.
[Example] The data length when "A171 UC24" and the numeric value 100
are transmitted as data is as follows (unit: byte):
AJ71 UC24
t t -
I /
10
bytes
b15
(E'
b B
b7
( ! ?
bl
bo
1 1
memory
.
I
V V
I
I
OOH
(3) Data area
The data area is a series of
1
byte data. Data of codes O O H to FFH can
be processed.
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