User`s manual

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CHAPTER 8 DATA COMMUNICATIONS USING
HALF-DUPLEX COMMUNICATIONS
For data communications between the Q series C24 and an external device using the RS-232 interface, it is set so that
the Q series C24 and the external device do not transmit data at the same time.
The QJ71C24 (N)-R2 can be set for each interface.
When the Q series C24 is started, full-duplex communications is set. The user can change the communications
method to match the specifications of the external device.
Since half-duplex communications does not have to be set in the following cases, you do not have to read this section.
● When data is only transmitted or receive during non procedure protocol data communications.
● When it is designated in the external device that no data transmission is performed from the external device to the Q
series C24 unless so directed by the Q series C24.
8.1 Half-duplex Communications
The following describes the differences between full-duplex communications and half-duplex communications.
Since the Q series C24 uses the communications method designated by the user to control programmable controller
CPU communications, control by sequence program is unnecessary.
(1) Full-duplex communications
This communication method uses telephone conversation format image to communicate data with the external
device.
The Q series C24 can receive data while transmitting data to the external device.
It can also transmit data while receiving data from the external device.
(2) Half-duplex communications
This communications method uses transceiver conversation format image to communicate data with the external
device.
If the Q series C24 receives data from the external device while transmitting data to the external device, it
controls data transmission and reception according to "Simultaneous transmission priority/non-priority
designation".
The Q series C24 does not transmit data while it is receiving data from the external device.
External device
Programmable
controller CPU
Data A-1
Data B-1
Data B-2
Data A-2
External device
Programmable
controller CPU
Data A-1
Data A-2
Data B-1 Data B-2