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Multi-Tech Systems MT2834MR6 6.3 Remote Digital Loopback Test (V.54 Loop 2)

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Chapter 6 - Testing and Troubleshooting

6.3 Remote Digital Loopback Test (V.54 Loop 2)

In this test, your modem must be online with another modem, such as another ZDX, that is set up to respond

to a request for remote digital loopback. With the ZDX, this ability to respond is controlled by the &T

command. AT&T4 enables the response to remote digital loopback; AT&T5 disables the response. The

modem defaults to &T5 on power-up, so this must be changed on the remote modem before initiating remote

digital loopback.

Initiate remote digital loopback with the ATU2 command, which places the remote modem in digital loopback

mode. Data from your computer or terminal are transmitted through your modem and over the phone line to

the remote modem, where they are then looped back to your modem. See Figure 6-2.

Figure 6-2. Remote digital loopback test.

6.3.1 Test Procedure

1. Arrange to have &T4 set on the remote test modem.

2. Open your communications software and go into terminal mode. Type AT and press ENTER; you should

get an

OK

message. Type AT&E0<CR> to disable error correction.

3. Dial the remote modem and establish your online connection.

4. Type the escape sequence (+++AT<CR> or <BREAK>AT<CR>) to bring your modem into command

mode while maintaining the connection with the remote modem.

5. Type ATU2 and press ENTER. The local modem responds to this command by transmitting an

unscrambled marking signal, which causes the remote modem to place itself in digital loopback mode.

Then the local modem exits command mode and enters online mode.

6. Enter data from your keyboard. For this test, typing multiple uppercase

U

characters is a good way to

send an alternating test pattern of binary ones and zeroes. Data received by the remote modem enters

its analog receiver, is converted to digital data, is reconverted into analog, and then is transmitted back to

your modem. Your modem passes this test if the data received on your monitor is the same as the data

entered from your keyboard.

7. To exit the test, enter an escape sequence (+++AT<CR> or <BREAK>AT<CR>), which returns the

modem to command mode. The modem should respond with an

OK

message. If you wish to stay on line

with the remote modem for normal data transmission, type ATO and press ENTER. If you wish to

terminate the call, type ATH and press ENTER to hang up.

Contents

Main Revision Date Description Contents Page Page Page Page 1.1 Introduction 1.2 Manual Organization 1.3 Description Owners Manual 1.4 FCC Regulations for Telephone Line Interconnection 1.4.1 FCC Fax Update 1.5 Canadian Limitations Notice 1.6 Technical Specifications Page 1.7 Power Supply 1.8 Modem LED Indicators Note: The MultiModemManager can perform the same function using software. 1.9 Busy Switch 1.10 MT2834MR6 Installation Notes Owners Manual Note: Such apparatus may have been approved subject to limitations in its use. 1.11 Safety Warnings Page Chapter 2 - Dialing and Answering 2.1 Introduction 2.2 Dial-Up Automatic Answering 2.3 Dial-Up Handshaking Details Chapter 2 - Dialing and Answering 2.4 Call Termination Page 3.1 Working with AT Commands 3.1.1 Modes of Operation 3.2.2 Command Structure 3.3.3 Command Editing Page Page Page 3.2 Dialing Commands 3.3 Dial Modifier Commands Page Page 3.4 Phone Number Memory Commands Page 3.5 Configuration Storage and Recall Commands Page 3.6 Modem Response (Result Code) Commands Page 3.7 Online Connection Commands Page Page Page 3.8 V.34 Commands 3.9 RS-232 Interface Commands Page 3.10 Error Correction and Data Compression Commands Page 3.11 Speed Conversion Commands Page 3.12 Immediate Action Commands Page 3.12 Flow Control Commands Page Page 3.13 Escape Sequences ATA S7 A 3.14 Remote Configuration Commands 3.15 Line Probe Commands 3.16 Diagnostic Commands Page 4.1 Introduction 4.2 S-Registers Page S7 S8 S10 S9 S9 S11 S11 S25 S24 &C Page Page 4.3 Reading and Assigning S-Register Values 4.3.1 Examples of Assigning Values 4.3.2 Examples of Reading Values 4.4 AT Commands Affecting S-Registers Page 5.1 Introduction 5.2 How V.42 Detects and Corrects Errors detected correction 5.3 Data Compression $BA0 &E5 &E4 $SB115200 #L 5.5 V.42 Mode Select Command ( #Ln #L0 #L 5.6 Modes of Operation &E0 &E1 5.6.3 Autoreliable Mode ( &E2 5.7 Flow Control 5.8 Modem-Initiated Flow Control &E5 &E4 5.8.2 Hardware Flow Control ( 5.8.1 XON/XOFF Flow Control ( &E13 5.9 Pacing ( &E9 5.9.3 Hewlett Packard ENQ/ACK Pacing ( &E11 5.10 Compression, Error Correction, Flow Control, and Pacing Commands 5.11 Result Codes 5.11.1 MNP Error Correction 5.11.2 LAP-M Error Correction 5.11.3 Data Compression 5.12 Speed Conversion $BA 5.12.1 Baud Adjust ( 5.12.2 Modem Baud Rate ($MB) 5.12.3 Serial Port Baud Rate ($SB) 5.13 Related Commands 5.13.1 Autoreliable Buffering ($A) 5.13.2 Maximum Block Size (&BS) 5.13.3 Autoreliable Fallback Character ($F) 5.13.4 Retransmit Count ($R) 5.14 Summary Page 6.1 Introduction Note: Loopback tests operate at all speeds except 300 bps. 6.2 Local Analog Loopback Test (V.54 Loop 3) 6.2.1 Test Procedure CONNECT 6.3 Remote Digital Loopback Test (V.54 Loop 2) 6.3.1 Test Procedure 6.4 Local Digital Loopback Test (V.54 Loop 2) 6.4.1 Test Procedure Page 7.1 Multi-Tech Systems, Inc. Warranty & Repairs Policies 7.1.1 Warranty mtsrepair@multitech.com www.multitech.com www.multitech.com. 7.1.3 International Customers (outside U.S.A. and Canada) 7.1.4 International Distributors 7.2 Repairs 7.2.1 Repair Procedures for U.S. and Canadian Customers 7.2.2 Repair Procedures for International Customers 7.2.3 Repair Procedures for International Distributors 7.2.4 Replacement Parts 7.3 Technical Support 7.4 Internet Site Page Appendix A ASCII Conversion Chart CTRL CODE HEX DEC CODE HEX DEC CODE HEX DEC CODE HEX DEC Appendix B Dial Pulses Tone Dial Frequencies Appendix C Result Code Summary CONNECT R or the letter &Q1 &Q Standard AT Result Codes ( L CONNECT Appendix D S-Register Summary Page Appendix E AT Command Summary Command Values Description Page &En n &E5 %Fn n $Fn n &F Page Page Page Page Page Appendix F RS-232C Interface Specifications Page Test Voltage (+V) Pin 9 (From modem) High Speed (HS) Pin 12 (From modem) Transmit Clock (TC) Pin 15 (From modem) Receive Clock (RC) Pin 17 (From modem) Data Terminal Ready (DTR) Pin 20 (To modem) Page Appendix G Cable and Connector Diagrams APPENDIX H Introduction to MultiTech Escape Methods How to Select an Escape Method Escape Method 1: +++AT<CR> Escape Method 2: <BREAK>AT<CR> S-Registers and Escape Sequence A S34 Aborting an Escape Sequence APPENDIX I Introduction to Remote Configuration Basic Procedure Setup Changing the Passwords Changing the Remote Escape Character Page Index A B C D E F G H I K L P Q R S T V W X