App - 28 App - 28
MELSEC-Q
APPENDIX
Appendix 7.2 Control by Signals
The following diagram shows the data flow when control by signals is enabled in the
communication channel.
Appendix 7.2.1 ER (DTR) control enabled
When the ER (DTR) control is enabled, ER (DTR) control signals of the RS-232C
interface are turned ON/OFF based on the size of the free area in the receive buffer
specified by the user, allowing the data transmission from the external device to the
communication module to be controlled and requested.
An ER control signal is turned OFF when the free area in the receive buffer becomes
one-fourth or less of the total space as data received from the external device is
stored.
An ER control signal is turned ON when the free area in the receive buffer becomes
three-fourths or more of the total space because of receive requests from the BASIC
program in the communication module.
A
D51H
(BASIC program)
ZOPEN • • • •
ZRECEIVE • • • •
Data
reception result
ZRECEIVE • • • •
Data
reception result
Data
reception result
ZRECEIVE • • • •
Communication module
Channel open 1
Receive buffer
(OS)
2
External device
The free area is
one-fourth or less.
The free area is
three-fourths or more.
Data
Data
ER control
signal
OFF
ER control
signal
ON
ER control
signal
ON
3
ZCLOSE
