Modem-Initiated Flow Control | Multi-Tech Systems MT2834MR6 specification

Chapter 5 - Error Correction, Data Compression, and Speed Conversion

5.8Modem-Initiated Flow Control

When operating in V.42 reliable mode, the MT2834MR6 stores data in a buffer as it is received. During periods of error-caused retransmissions or compression slowdowns, this buffer may fill up. To prevent buffer overflow and subsequent loss of data, the modem uses flow control to signal the computer attached to its RS- 232 port that the modem buffer is close to being full. This causes the computer to pause in its data transmission until the modem is able to empty its buffer sufficiently to accept more data, at which time the modem signals the computer that it may resume transmission.

The MT2834MR6 can use either of two methods of modem-initiated flow control: software flow control, which uses special XON and XOFF characters in the data transmissions, and hardware flow control, which uses the CTS output on the RS-232 interface. Most terminals and computers support one or both of these methods.

5.8.1 XON/XOFF Flow Control (&E5)

In this method, control characters known as XON and XOFF are inserted by the modem into the flow of data from the serial port. XOFF (CTRL-S), stops the flow of data, and XON (CTRL-Q), restarts it. XOFF/XON flow control is not recommended for binary data, because an XOFF character could be part of the data, and would halt data flow.

5.8.2 Hardware Flow Control (&E4)

With hardware flow control, the modem uses the RS-232 interface to control the flow of data on the serial port. The CTS (Clear to Send) signal on Pin 5 of the RS-232 interface is brought low to stop the flow of data, and is brought high to restart it.

When you select hardware flow control as your flow control method, you select it also for pacing. The difference between the two is that flow control uses the CTS output signal, while pacing uses the RTS input signal.

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Multi-Tech Systems MT2834MR6 manual Modem-Initiated Flow Control, 1 XON/XOFF Flow Control &E5, Hardware Flow Control &E4

Contents

User Guide Revision Date Description Trademarks Contents Registers Warranty & Service Index 116 Introduction Introduction Manual Organization Description FCC Fax Update FCC Regulations for Telephone Line Interconnection Canadian Limitations Notice Technical Specifications Diagnostics Bell 103/113300 bps Fax Carrier Power Supply Modem LED Indicators Busy SwitchSpeed Data Rate bps LED State 10 MT2834MR6 Installation Notes Safety Warnings Dialing and Answering Dial-Up Automatic Answering Dial-Up Handshaking Details Call Termination AT Commands Working with AT Commands Modes of Operation Command Structure Command Editing AT Commands Baud adjust Flow control disabledModem baud rate Serial port baud rate Force answer mode Alternate out-of-band escape sequenceEscape sequence selection Go back online Dialing Commands Default noneDial = phone number Dial Modifier Commands Default PDefault R0 Pulse or Tone Dialing Or 4 through 255 seconds International models ATDT1028806127853500 $123456789 Phone Number Memory Commands NdNe Number Linking = 0 or = 1 or Default none T14082345678 P9,T14089876543 Configuration Storage and Recall Commands Default &W1Default &F8 = 0, 8, or AT&W1 default ATZAT&F8&W0 AT&F9&W0 Modem Response Result Code Commands Default Default &A0Result Codes and Call Progress Selection Online Connection Commands #An Auto Speed Detection Default #A0Default B0 DCn AT Command Control = 0 or Default %DC0 CDn Cleardown at Disconnect = 0 or Default &CD0 DTn Dtmf Detection = 0 or Default DT0#Fn Fallback Modes = 0, 1, or Default #F2 Default &G0 models outside U.K Default *H0Default &P0 Models outside U.K G2 U.K. models only #T0 disables TCM #T1 enables TCMDefault Y0 Issued V.34 Commands RS-232 Interface Commands Default &C1Default &D2 Default &R1 Default &S1 Go high againS0 forces DSR high S1 allows DSR to act normally, that is, to follow CD Error Correction and Data Compression Commands Default &E1Default &E15 #Ln Error Correction Modes Default #L0 $En Error Correction at 300 bps = 0 or Default $E0 $An Autoreliable Buffering = 0 or Default $A0$Rn Retransmit Count = 0 or Default $R0 Speed Conversion Commands $SBn Serial Port Baud Rate = speed Default $SB57600 $SB300$SB1200 $SB2400 Immediate Action Commands Rate Renegotiation Flow Control Commands BSn Maximum Reliable Block Size = 0 or Default &BS1$EBn Asynchronous Word Length = 0 or Default $EB0 Flow Control Disable Default &E6 Default &E8Non-Error Correction Mode Flow Control Default &E10 Default &E13 #Xn Number of Xoff Characters Sent = 0 or Default #X0Pacing Computer-Initiated Flow Control = 12 or Escape Sequences Remote Configuration Commands Atcr Remote Configuration Escape Sequence Line Probe Commands Diagnostic Commands Registers Registers Default 13 M Default 10 JDefault 8 H Return Character Time for Carrier Abort Timer Default 45 North America and InternationalUnit 1 second Range 1-255 U.S.A Maximum S11 value is 255 ms 255 units Registers Registers Reading and Assigning S-Register Values Examples of Assigning ValuesExamples of Reading Values AT Commands Affecting S-Registers Error Correction, Data Compression & Speed Conversion Error Correction, Data Compression, and Speed Conversion How V.42 Detects and Corrects Errors Data Compression MNP Classes V.42 Mode Select Command #L 1 #L0 Command2 #L1 Command 3 #L2 Command Non-Error Correction Mode &E0 Reliable Mode &E2Autoreliable Mode &E1 Modes of Operation Flow Control Flow control and pacing Modem-Initiated Flow Control 1 XON/XOFF Flow Control &E5Hardware Flow Control &E4 Non-Error Correction Mode Flow Control &E10 and &E11 Pacing &E131 XON/XOFF Pass-Through &E7 Hewlett Packard ENQ/ACK Pacing &E9 10.1 V.42 Error Correction Modes Non-Error Correction Mode Flow ControlModem-Initiated Flow Control 10.3 XON/XOFF Pass-Through MNP Error Correction LAP-M Error CorrectionResult Codes Speed Conversion Baud Adjust $BA Modem Baud Rate $MB Serial Port Baud Rate $SB Related Commands Autoreliable Buffering $AMaximum Block Size &BS Autoreliable Fallback Character $F 13.5 V.42 Error Correction at 300 bps $E SummaryRetransmit Count $R Testing & Troubleshooting Testing and Troubleshooting Test Procedure Local Analog Loopback Test V.54 Loop Remote Digital Loopback Test V.54 Loop Remote digital loopback test Local Digital Loopback Test V.54 Loop Local digital loopback test Warranty & Service Multi-Tech Systems, Inc. Warranty & Repairs Policies Warranty2 U.S. and Canadian Customers International Customers outside U.S.A. and Canada International Distributors Repair Procedures for U.S. and Canadian Customers Repair Procedures for International CustomersRepairs Technical Support Internet SiteCountry Telephone Appendices Ascii Conversion Chart Appendix a Appendix B Dial Pulses Tone Dial Frequencies Figure B-2. Standard Dtmf frequencies Appendix C Result Code Summary Standard AT Result Codes &Q1 Register Unit Range Default Description Appendix DRegister Summary S34 AT Command Summary Command Values DescriptionAppendix E CDn 100 101 102 103 104 105 RS-232C Interface Specifications Signal Information Negative PositiveAppendix F Functional Description of the RS-232C Signals Transmitted Data TD Pin 2 To modem Test Voltage +V Pin From modem External Transmit Clock XTC Pin To modem Cable and Connector Diagrams Appendix G Appendix H Introduction to MultiTech Escape Methods How to Select an Escape Method Escape Method 1 +++ATCR Registers and Escape Sequence Aborting an Escape Sequence Introduction to Remote Configuration Basic ProcedureSetup Changing the Passwords Changing the Remote Escape Character Index Index 118 119 120 121 122 S000326A