Considerations For Using The Modem Function - Mitsubishi Electric MELSEC iQ-R Series User Manual

Considerations for using the modem function

Considerations for using the modem function to perform data communication with a target device via public line are shown
below.
Modem connection and disconnection
When performing data communication with a target device, it must be predetermined which station is to perform the line
connection (dialing) and disconnection processing with the target device as well as the timings.
Reception data before connection completion
Until the connection processing to the modem is completed, the received data other than modem commands is ignored (read
and discarded) at the interface that uses the modem function.
(Example) C24 will ignore the data even when an MC protocol command message is received.
Transmission control
Delays may occur in transmission controls to notify the data reception capability at the host station to the target device.
The amount of transmitted/received data and the interval must be determined beforehand in order to prevent any conditions in
which the target device cannot receive transmitted data.
When transmitting/receiving data in the nonprocedural protocol, the procedure must also be predetermined.
Priority of data communication
The data transmission/reception processing with the target device after line connection has been established is performed in
the order of the processing request occurrence.
At the same time, when the line disconnection processing or data transmission/reception (including data transmission
processing, reception processing and flash ROM access processing) occurs, the line disconnection processing has the
priority.
Data communication time
The data transmission/reception time after line connection has been established with the target device is the total time of the
transmission time between C24 and modem/TA, between modem and TA, and between modem/TA and target device.
When communicating via the MC protocol, the transmission time (such as T0 and T3) must include the transmission time
between the modem/TA on the C24 side and the target device.
For details, refer to the following manual.
 MELSEC Communication Protocol Reference Manual
Initial Settings
The data for connection, which is used for the modem function, can be registered as follows depending on how to set.
Set the telephone number and message within the allowable number of registration characters for modem/TA.
■Registering using Engineering tool
• Up to 254 bytes can be set for comments. (Not used for control.)
• Up to 62 bytes can be set for telephone number.
■Registering by the CPU module (program)
• Comments cannot be set.
• Up to 18 bytes can be set for telephone number.
Programmable controller CPU monitoring function
For considerations for transmitting monitored results with the modem function, refer to the following section.
Page 147 Modem connection error
7 COMMUNICATIONS BY THE MODEM FUNCTION
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7.3 Specifications of Modem Function