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7 COMMUNICATIONS BY THE MODEM FUNCTION
7.3 Specifications of Modem Function
CPU module side countermeasures against unauthorized access from a target device
The following is an example of performing, on the programmable controller CPU side, the line disconnect processing against
the target device and prohibiting receive via a modem when the number of "remote password mismatch" detected by the C24
remote password check function exceeds the number set by the user.
• Determine at the user side the count and accumulated count for notification when a remote password mismatch occurs in
the unlock processing from external devices with respect to the remote password set in the CPU module.
(Page 165 Details of buffer memory (for the remote password function))
• Set the above counts to the items below for the module parameters in order for C24 to operate, and register them in C24.
Set in "Remote password mismatch notification count."
Set in "Remote password mismatch notification accumulated count."
• In addition to initialization commands used in normal modem initialization, specify "No automatic receive" and additionally
register the modem initialization command for this step to C24. (No automatic receive: This is the setting to prohibit line
connection from the target device.)
• Constantly monitor the rise (OFF ON) of the 'CH Error occurrence' (XE/ XF) when connecting the line to the target
device using the modem function after the system begins operating.
• Monitor the following buffer memory when the error occurred signal turns ON.
'MC protocol send error code' (Un\G602)
• Perform the line disconnect processing to the target device when the error code stored in the above buffer memory is
7FE8H.
(Use the 'Modem disconnection request' (Y12).)
• After the above line disconnection processing is completed, specify the modem initialization command for which "No
automatic receive" has been specified and perform modem initialization only. (Page 199 Data communication)
• Describe the above occurrence to the system manager and take necessary measures.
■Program example
When the number of times a remote password mismatch occurred exceeds the notification accumulated count setting value
during the remote password unlock processing in communication using MC protocol with the C24 CH1 side interface used.
Category Label name Description Device
Module label C24_1.stnCH1.bSts_Error CH1 Error occurrence X0E
C24_1.bSts_ModemInitializationCompletion Modem initialization completion X10
C24_1.bSts_ConnectionProcessing Connection X12
C24_1.bSts_Initialization_Connection_AbnormalCompletion Initialization/connection abnormal
completion
X13
C24_1.bSts_DisconnectionCompletion Modem disconnection completion X14
C24_1.bSts_UnitReady Module READY X1E
C24_1.bSts_WatchdogTimerError Watchdog timer error X1F
C24_1.bSet_Req_ModemInitialization Modem initialization request Y10
C24_1.bSet_Req_Disconnection Modem disconnection request Y12
C24_1.uSet_DataNum_Initialization_ModemFunction1_D Data No. for initialization designation U0\G52
C24_1.uErrorCode_ModemFunction_D Modern function error code U0\G545
C24_1.stnCH1.uErrorCode_MC_ProtocolTransmissionErrCode_
D
Protocol transmission error code U0\G602
C24_1.wnForUserRegistrationNo8005H_D[0] User registration number 8005H U0\G7076
C24_1.uCount_RemotePasswordAccumulatedUnlockProcNormal
_D
Accumulated count of unlock process
normal completion
U0\G8955
Label to be defined Define the global label as shown below.
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