6 DATA COMMUNICATION USING THE NON PROCEDURE PROTOCOL MELSEC-Q

(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 Q series C24 buffer memory (receive data storage area).

2)The data is stored to the receive data storage area in low address (L) (H), next address (L) (H) order.

Under the following conditions, when the receive data count is an odd byte, 00H 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 arbitrary data area "ABCDEFG123" was stored

(The receive area is the default value.)

 

 

 

 

 

Q series C24

 

 

 

 

 

 

 

CH1

Buffer memory

 

 

 

 

 

address

 

 

 

 

 

600H

 

 

5 or 10

 

 

 

 

 

601H

 

(B)

(A)

 

 

 

 

 

 

 

42H

41H

 

Head

 

602H

 

(D)

(C)

 

 

 

 

 

 

 

44H

43H

 

 

OS area

 

603H

 

(F)

(E)

 

"321GFEDCBA"

 

 

 

 

46H

45H

From external

 

 

604H

 

(1)

(G)

device

 

 

 

 

 

 

31H

47H

 

 

 

 

 

605H

 

(3)

(2)

 

 

 

 

 

 

 

33H

32H

( 1)

 

606H

 

 

 

 

 

 

 

 

……

 

 

 

 

 

 

 

 

 

 

 

 

Receive data count storage area

Receive data storage area

The receive data is stored in low address (L) → (H), next address

(L) → (H) order in the order in which it is received.

1 The OS area of the Q series C24 shown in the above diagram 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 PLC CPU. (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 signal does not turn OFF):

•When DTR control is set, the 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 communication error information storage area (address: 201H/202H) 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, see Chapter 7 of the User's Manual (Application).

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