Communication with External Devices
FP2 Serial Data Unit
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4.2 Programming When Data is Sent
4.2 Programming When Data is Sent
4.2.1 How Timings and Flags (Contacts) Work
How communication is controlled
With the serial data unit, control based on the contact on and off signals is the most
secure way of carrying out data sending and reception, regardless of the position of the
slot in which the unit has been installed.
Communication is carried out using two contacts when data is sent and two contacts
when it is received, for each port.
Time chart when data is sent
Sent data of RS232C port
Operation
steps
Executed by
serial data unit
Executed by
CPU unit
1. Sent data is
created.
2. Data is written to shared memory.
3. Data is sent
(Sending directive flag goes on).
4. Sending completed flag goes on.
5. Sent buffer is cleared.
6. Sending completed flag goes off.
Sending Completed
(X0)
Sending
directive (Y10)
Shared memory of
serial data unit
Data register of
CPU unit
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