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APPENDICES
MELSEC-A
APPENDIX 6. Precautions During Communications When Using RS-422 Interface
(1)
The following figure shows the hardware structure for the data trans-
mission from the AJ71
C24
to the computer.
Received data
High
impedance
control
AJ71 CZ4
AJ71C24
Send Circuit
(2)
Data transmission methods
When each station of the AJ71C24 is not transmitting data, set the
transmission line to the high impedance state so that one send data
does not interfere with other send data in a multidrop link.
When all stations transmit data, the high impedance state must be
canceled. Then, after transmitting a mark consisting of
2
or more
characters, each station transmits data.
This method applies also to a 1:1 link system
A mark consisting of
2 or
more characters
High impedance
state
High impedance state
- v - / J
Composition of 1 character
S e n d d a t a k ~
-
- - -
Character
Stop bit (1 to 2 bits)
Stalt bit$ bit)
pArity
(0
to 1 bit)
(7 to 8 bits)
Transmission from the
AJ71C24
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