Table of Contents
Advertisement
APPENDIX
Appendix 7 Details of Communication Control
Appendix 7.1 DC1/DC3 Control
Appendix 7.1.1 DC1/DC3 transmission control enabled
1 A DC1 control signal is not sent to the external device when the communication channel is opened. The
status of the receive buffer is the same as when the DC1 control signal is sent, however.
2 After a DC3 control signal is sent, the received data is stored in the receive buffer until the free area in the
receive buffer runs out.
App - 26
The following diagram shows the data flow when the DC1/DC3 control is enabled in
the communication channel.
When the DC1/DC3 control is enabled, DC1/DC3 control signals are sent to an
external device 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.
A DC3 control signal is sent to the external device 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.
A DC1 control signal is sent to the external device 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)
Channel open
ZOPEN • • • •
ZRECEIVE • • • •
Data
The free area is
reception result
one-fourth or less.
ZRECEIVE • • • •
Data
reception result
ZRECEIVE • • • •
Data
reception result
In order to enable the DC1/DC3 transmission control, specify 1 or higher for the receive
buffer specification when opening the communication channel.
Communication module
(OS)
1
Receive buffer
Data
DC3 control signal
2
The free area is
DC1 control signal
one-fourth or less.
Data
MELSEC-Q
External device
App - 26
Advertisement
Table of Contents
