NAiS FP2, Technical Manual

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2-10
Precaution when using RS485 port
RS485 communication is a communication method to perform sending and receiving by two-wire system.
Therefore, only one device enables to send data in the communication line at the same time.
Multi Communication Unit (MCU) can send back responses (send data) instantaneously for the
transmitted data from other devices .
However, depending on other devices connected, it may need a time to open the communication line. In
this case, data cannot be sent correctly as the transmitted data from MCU and the transmitted line of the
other devices clash.
(The above figure shows an example that the transmission “a” and “b” clash.)
In this case, it is necessary to adjust the time until starting sending at MCU side, to enable the normal
transmission. The time taken until starting the transmission is called “send waiting time”, and specified
with the memory switch.
1. MCU setting
2. F159 (MTRN) instruciton
Specify the necessary wating time for the “send waiting time” area.
Example:
With the RS232C/RS485 converter SI35 manufactured by Lineeye Co., Ltd., adjust the response time by
this instruction if necessary.
Reference: <9.2 Communication Condition settings and Monitors>
<4.4.3 Memory Switch MCU settings>