Advantech PCM-3601 user manual Modem Operation and Response Codes, Command State and Data State

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Chapter 3

Modem Operation and Response Codes

This chapter describes modem states, commands and response codes and explains how to issue commands to the modem.

3.1Command State and Data State

During operation, your modem is either in command state or data state. The figure below shows the relationships between the two states and how to enter and abort from each of them.

In command state, the modem interprets all the characters it receives as commands. The command state may either be on-line or off-line. When the modem is holding a connection with a remote modem or when it is in an analog loopback test, it is on-line. Otherwise, it is off-line.

In data state, the modem is a transparent receiving and sending device. It assumes everything it receives (except the escape sequence) as data and conveys them to the local computer or remote system.

3.2The Escape Sequence (+++)

The escape sequence instructs the modem to leave (escape) the data state and enter the command state, without breaking the connection. It is the only data string that is interpreted as a command when the modem is in data state.

After switching to command state, the user can issue further commands, such as changing parameter settings, etc. To resume data state, simply issue ATO.

The escape command in default is three consecutive “+” characters. For the modem to distinguish the escape command from the data, a certain duration of guard time is defined to exist both prior to and after the three consecutive escape characters. The escape sequence includes a guard time, three consecutive escape characters, and a guard time, in that order.

The default guard time is 1 second. It can be changed by assigning a different value to register S12.

In the same manner, you may change the escape character to a

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Contents PCM-3601 Copyright notice Chapter Unpacking and InstallationFeature Fdsp Full -duplex speakerphone Data modem throughput up to 115.2K bpsNvram directory and stored profiles Error Correction & Data CompressionVoice/audio mode PackageUnpacking the Modem Look at the Modem CardPC/104 FaxModem Card Setting the COM Port and Interrupt of the Modem Card Installing the Modem CardSerial Port and Interrupt of the Modem Card Testing the Telephone Line Prior to Connection Communications Software ConfigurationSoftware Configuration Tips AT&P0DP Getting StartedModem Fundamentals Modem BasicsData Format Communications Protocol Speeds of the ModemOn-Line Speed DCE Speed Serial Port Speed DTE SpeedError-Correction and Data Compression Ecdc Flow Control Non-Volatile Memory NvramMajor Stored Configuration Profile Major SCP Factory Default Profile FDPStored Configuration Profile SCP Active Configuration Area ACAStored Telephone Numbers STN Command State and Data State Modem Operation and Response CodesEscape Sequence +++ Issuing Commands Command BufferDeleting Commands Modem AT Response Codes Dial Commands and Dial Modifiers AT CommandsPrefix, Repeat and Escape Commands Operation CommandsW1 Enable V.42 response codes, display DCE speed M0 Set modem for async operation P0 M/B ratio 39/61USA Call Back Security Command Set Option Lease Line/Dial Line command set OptionLease Line Backup Dial Line command set Option Display Dialing Number if AT&In Command supportOption Auto Dial/Redial mode Option42bis and MNP Command Set Break ControlData Compression Ecdc Operation Mode SelectionMNP Response Code Option Automatic RetrainAppendix a Modem RegisterRegister Summary 1711h XON Character S33 255 Appendix B Result Codes+FCERROR Short Form Long Form Fax Command Codes Fax Class Fax Class II CommandsAppendix C +FDIS Installation of Modem Driver in Win 95/98 Appendix D
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