3Com 56K Hardware and Software Flow Control

11-2 CHAPTER 11: FLOW CONTROL

Hardware and Software Flow Control

There are two kinds of flow control: hardware and softwar e. Business

Modems support both, but your computer and communications software

must also support the kind of flow control you choose.

Hardware Flow

Control Business Modems implement hardware flow control by detecting that a

buffer is 90% full and then interrupting the Clear to Send (CTS) signal to

stop the flow of data. When the buffer drops back to 50% full, the

Business Modem sends CTS to restart the flow of data.

Software Flow

Control Business Modems implement software flow control by detecting that a

buffer is 90% full and then sending special characters in the data stream

to stop the flow of data. When the buffer drops back to 50% full, the

Business Modem sends special characters in the data stream to restart the

flow of data.

The problem with software flow control is that the characters used to

stop (<Ctrl>Q) and start (<Ctrl>S) the flow of data can occur naturally in

the data flow. Enabling software flow control instructs the Business

Modem to recognize and act on these characters, even if they are not

intended to control the data flow.

Using software flow control may prove satisfactory if you're transferring

text files only.

The start command is called XON (for transmit on) and the stop

command is called XOFF (transmit off). You can change the ch aracters

used. See Registers S22 and S23 in Appendix B, Alphabetic Command

Summary.

Contents

Main 3Com Corporation 3800 Golf Rd. Rolling Meadows, Illinois 60008 C A BOUT T HIS G 1 2 3 4 5 6 7 8 9 R 10 11 12 T 13 14 15 16 A B C D E F G H I G J ABOUT THIS GUIDE Conventions Table 1 Notice Icons Table 2 Text Conventions n Page Page 1 Windows 95/98 Page Page Page Page Page Page Windows NT 4.0 and Later Page Page Page Macintosh Page Page Page Page Other Operating Systems Page 2 Overview Basic AT commands Using S-Registers Page Understanding bit-mapped S-Registers 3 This chapter contains information about Command and Online Modes DO NOT type AT before +++ or <ENTER> after the command Page Controlling Local Echo Data and Fax Modes Page Page 4 H ANGING U Dialing Page Carrier Loss Redial Answering Calls Making International calls Call Detection Caller ID Functions Page Page Distinctive Ring Support Page Page 5 Overview Saving a Phone Number to NVRAM Working with Flash Memory Page 6 D This chapter contains information about: Result Code Display Commands and in what format they are displayed Additional Result Code Subsets 7 S Data Terminal Ready Data Set Ready Carrier Detect Page 8 Overview Serial Port Rates Your software may use terms such as locked serial port (fixed rate) or autobaud (variable rate). The serial port rate MUST be equal to or higher than the Connection rate (&Nn). Connection Rates Controlling Link Speeds with &N and &U Page &N and &U Command Values Use the following table for a complete list of &N and &U link speeds and their associated indexes: Setting DTE Rate to 230 Kbps Page 9 THE BUSINESS MODEM REMOTELY Overview Setting Up Remote Access Page Accessing the Host Page Page Page Page Page 10 Overview Setting up Dial Security Page Page Page Page Maintaining Security Accounts What the Guest User Needs to Do Configuring Dial Security Remotely Page 11 Overview Hardware and Software Flow Control Received Data Flow Control Page Transmit-Data Flow Control by its attached computer. Page 12 DATA COMPRESSION, AND T Handshaking Page V.90 Capabilities Other Protocols Page Error Control Page Page Data Compression Getting Maximum Throughput Page Page Page 13 S Querying Overview Page Displaying Help Page 14 Overview Testing the Business Modem using AT&T n Page Page Page Page Page Page Testing the Business Modem using S-Resister 16 Page Page Page 15 Problems That Occur Before Connecting Page Page Problems that Occur After Connecting Page Page Page Page 16 Overview Checking Your Business Modems Software Version Getting New Operating Software Sending New Software to your modem Page If Your Modem Doesnt Respond A Understanding Bit-Mapped S-Registers How bits are mapped to decimal values Page Using Bits Using Decimal Value s Default S-Register Settings * Bit-mapped registers have up to eight functions. A complete list of S-Registers Page Page Page Page Page Page Page B S Basic Command Set 1 Wait 1 second after sending the last item of data. Optional parameters: Page See Appendix A, S-Registers for a listing of all the S-Registers. Ampersand (&) The serial port rate MUST be equal to or higher than the &Nn rate. Page Page Page Page Page Percent (%) Using%C1 will not reverse any changes that you wrote to NVRAM (with &W) or forced (with%C2). Octothorpe (#) Page C Hardware Flow Control template send AT&F1 to your modem. Page Software Flow control template send AT&F2 to the modem. No Flow Control send AT&F0 to the modem. Page Page D S Result Code Meanings Result Codes Sets for Xn Value s Result Code s X0 X1 X2 X3 X4 X5 X6 X7 E Technical Specifications is also compatible with many nonstandard schemes. The following schemes are supported: Modulation clients can call into your Business Modem to get 56K connections Page Additional Specifications Page Page Page F F-2 APPENDIX F: ASCII CHART G P the following optional Class 2.0 fax commands: Fax Service Class 1 Commands FAX Service Class 2.0 Commands Fax Mode Flow Control Setting FCC Notice Notes H This appendix explains how to view the twelve LEDs on the front of your Business Modem. Page I S-Registers Page Page Page Page Page Page Page J 3COM CORPORATION LIMITED WARRANTY Page Page Notices FCC Registration FCC Notice FCC Notice: Radio and Television Interference Page G