Communication Error "Sio - Mitsubishi QJ71C24N User Manual

11 TROUBLESHOOTING

11.3.11 Communication error "SIO"

Symptom
• Data does not match the
• Transmission rate is too
• Data larger than the
• Communication
error signal "SIO"
turned on.
• With a multidrop link, two
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Cause
stop bit setting.
fast and the next data is
transmitted before the Q
series C24 completes
processing of the receive
data.
receive buffer size was
received.
or more devices
transmitted data at the
same time.
Corrective action
• Check if the Q series C24 and external device
settings are the same.
• Decrease the transmission rate and restart
data communications.
• Use DTR and DC control and interrupt
transmission before the buffer becomes full.
Perform RS and CS control when the modem
function is used.
• Increase the transmission interval and provide
an ample programmable controller CPU read
processing time.
Note
• The non procedure protocol stores the data
received up to first the end code received,
or fixed length data, to the non procedure
receive buffer memory and turns on the
Read Request signal to the programmable
controller CPU.
If the next data is sent while the Read
Request signal is ON, the data is
temporarily stored to the OS receive buffer.
When the OS receive buffer becomes full,
the Q series C24 skips the rest of the data
and turns on the "SIO" LED.
• Connect the external devices and the Q series
C24 in a 1:1 configuration and perform a
communications test. Since data is
transmitted simultaneously from two or more
devices with a multidrop link when normal
communications among all the devices is
possible, interlock the devices so that cannot
transmit simultaneously.
MELSEC-Q
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