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4. COMMUNICATIONS USING A DEDICATED
PROTOCOL
MELSEC
QnA
4.9.3
On-demand function setting items
The following describes the items which are set when the on- demand function is used in data
communications.
Buffer memories used by on-demand function
Address
Description
Name
96H
Designates the send data length units. Word/byte designation
AOH
On-demand buffer memory
the data
to
be sent by the on-demand function.
area
nate the head address of the buffer memory storing head address d
Uses the sequence program
TO
instruction
to
desig-
A i
H
error, the
AC71 QC24
writes the error code
to
this
area
When the on-demand function generates a data send
On-demand error storage
256H
function.
nate the data length
to
be sent by the on-demand
designation area
Uses the sequence program
TO
Instruction
to
desig-
On-demand data length
area.
IO:
No
error Nonzero:
Error
400H
I
User
area
I
The
user
data
sent
to
the external device is
written
to
I
to
I
I
this
area.
On-demand handshake signals
The on-demand handshake signals are signals that are turned ON when the AJ71 QC24 sends
a Request to Send data from the PC CPU to an external device and are turned OFF at the end
of transmission of the designated data by the AJ71QC24. The on-demand handshake signals
are used to interlock the devices so that multiple on- demand requests are not issued at the
same time.
Signal Timing
Contents
XnO
On-demand send normal
end
-
Xn 1
On-demand send error
detected
~
Xn2
On-demand send under-
way
I
Y n O
On-demand
request
to
sequence
program
Turned
OFF
by
I
lsend
Turned ON by sequence program
I
(Note) "n" of XnO, etc. is the I/O No. determined by the slot into which the AJ71 QC24. is inserted.
With the system configuration shown below, the AC71 QC24 is allocated to X.Y80-9F.
0
1
2
3
4
(Slot No.)
Power
QC24
iAY421
(AX421
CPU
supply
pJ71
Output
Input
QnA
Vacant Vacant
XnO=X80
64
Xn2=X82
polnts
pdnts
points
Xnl =X81
32
64
YnO=Y80
X00
Y40 X.Y80
\
\
\
X3F
Y7F X.YSF
When the AJ71 QC24 dedicated command (ONDEMAND) is used in data communications, data
can be sent and received without being aware of the buffer memories and on-dernand hand-
shake signals described above.
4
-
37
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