Mitsubishi A Series - Page 16

1, GENERAL DESCRIPTION
MELSEC-A
(b) Bidirectional communications
1) Data communications can be initiated by a PC CPU
Data communications can be initiated by a computer or any PC
CPU. Data can be transmitted from a PC CPU to an external
device by using the TO instruction in the sequence program to
write data to the buffer memory.
The data send operation is completed when the response mes-
sage to the sent (received) data is received from the computer.
The result of the send (normal end/error) is stored
in the buffer
memory and can be read out.
The data received from the computer can be read with the
FROM
instruction of the sequence program.
(When data is transmitted by an AJ71C24)
TO instruction Data send
Xno ON
Reapomereceke
PC CPU
Computer
AJ71 C24
(Send complasd)
FROM instruction
-
(Send result)
2) Data length is set within the send message
Data. length is set within the send message when the data is
transmitted to a device.
The receiving side recognizes the data length by the send mes-
sage.
Data
-pq check
I I I I I
1 T
The send data of the AJ71 C24 is processed as follows.
ENQ: ..................... Added to the head.
Data length: ........ The rend data length set in the buffermemory is transmitted,
Data: ..................... The send data stored in the buffer memoryir transmitted.
Sum check: ......... Computed with the sum checking range in a message.
The data transmitted by a computer and received by an AJ71 C24
is processed as follows.
ENQ: ..................... Checked and removed from the received data.
Data length: ........ Stored in the buffer memory as the received data length.
Data: ..................... Stored in the buffer memory as the received data.
Sum check: ......... Checked and removed from the received data.
3) Variable communications memory area
The user memory area can be allocated to suit the purposes and
applications of the data transmission.
1-6
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com