3Com 56K Command Reference Manual page 8

Digital Loopback Testing (AT&T3) ...............................................14-5
Remote Digital Loopback Testing (AT&T6, AT&T7) ......................14-6
Granting a Digital Loopback Test Request (AT&T4) .....................14-6
Canceling All Digital Loopback Test Requests (&T5) ....................14-6
Testing Using Keyboard Data (AT&T6) ........................................14-7
Testing Using a Built-in Test Pattern (AT&T7) ...............................14-8
Testing the Business Modem using S-Resister 16 .............................14-9
Analog Loopback (AL) S16=1D ..................................................14-9
Testing Using Keyboard Data (ATS16=8) ..................................14-10
Testing Using a Built-in Test Pattern (ATS16=4) .........................14-11
Ending Testing That Uses the Test Pattern ......................................14-11
15
T
ROUBLESHOOTING
Problems That Occur Before Connecting .........................................15-1
No response to AT .....................................................................15-1
The Business Modem won't dial .................................................15-2
Double characters are appearing on your monitor ......................15-3
After you dial, the Business Modem reports NO CARRIER and then hangs up
15-3
Hear ringing but the Business Modem won't answer .................15-3
The Business Modem acts as though a data link has been established, but
no call was received, ..................................................................15-3
The Business Modem behaves as if <Enter> were pressed when you don't
press any keys ............................................................................15-3
Problems that Occur After Connecting ...........................................15-4
Your screen displays random or "garbage" characters ...............15-4
Many CRC errors .......................................................................15-4
Mainframe computer keeps dropping your connection ..............15-5
Bad faxes or can't fax ................................................................15-5
Both devices exchange carrier signals, but fail to establish a
communications link ..................................................................15-5
Errors during software download ...............................................15-6
If You Still Have Problems ...............................................................15-6
16
U Y
PGRADING
Overview ........................................................................................16-1
Checking Your Business Modem's Software Version ........................16-1
M
OUR ODEM