Mitsubishi MELSEC LJ71C24, User Manual

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10 DATA COMMUNICATION USING THE NONPROCEDURAL PROTOCOL
(2) Receive data list
The following describes the data list when data received from an external device
is stored to the receive area.
1) The receive message is stored to the C24 buffer memory (receive data
storage area).
2) The data is stored to the receive data storage area in the order of low
address (L) (H), next address (L) (H).
Under the following conditions, when the receive data count is an odd
byte, 00
H
is stored in the upper byte of the final data storage position:
• When the unit for the received data count is designated in bytes.
• When data reception is performed using the receive complete code.
(Example) When receive data "ABCDEFG123" was stored (The receive area
is the default.)
600H
601H
602H
603H
604H
605H
606H
(B)
42H
(C)
43H (D)
44H
(E)
45H (F)
46H
(G)
47H (1)
31H
(2)
32H (3)
33H
(A)
41H
"321GFEDCBA"
From external device
Head
OS area
C24
( 1)
Buffer memory
5 or 10
CH1
address
Receive data count storage area
Receive data storage area
The receive data are stored
in the order of low address (L) (H),
next address (L) (H)
as they were received.
1 The OS area of the C24 shown in the above figure is the memory (8448
bytes) that temporarily stores the data to be received while a request for
the reading of the receive data is being made to the CPU module. (The
user cannot read the receive data in the OS area).
When the sequence program finishes reading the receive data in the
buffer memory in response to the read request, the receive data in the
OS area, and any succeeding receive data, is stored successively in the
receive area of the buffer memory when the next read request is issued.
Also, when the OS area's free space, which stores the receive data, is
reduced to 64 bytes default value or less, a request to discontinue data
reception from the external device is issued by the following transmission
control (the RS(RTS) signal does not turn OFF):
• When DTR control is set, the ER(DTR) signal turns OFF.
• When DC1/DC3 control is set, DC3 is sent.
When there is no more free space in the OS area to store receive data,
an SIO error occurs and the SIO information bit in the LED ON status
and communication error status (address: 201
H
/202
H
) in the buffer
memory turns ON. In that case, succeeding receive data is discarded
until a free space becomes available in the OS area.
For more details on the transmission control, refer to the User's
Manual (Application).