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Modem Diagnostic Screens Quick-Reference:
3Com/USR  Lucent  Rockwell/Conexant  Cirrus  PCTel   UD - Unimodem Diagnostics

A high connect speed is no good if it doesn't hold. Retrains are bad! To find out if you have had retrains, or if your modem dropped to a lower speed after your initial connect, you need to examine the Modem Diagnostic Screens after you finish a connection using HyperTerminal or Modemchk.

With newer modems that support the UD (Unimodem Diagnostics), and Windows 2000 or XP, it's now possible to automate logging of modem diagnostic results after each call - see the Unimodem Diagnostics section below.

3Com/USR modems give you the most complete information, and you can usually tell if your line has more than 1 a/d conversion. See 3Com Diagnostic Screens for the data and what it means. 3Com/USR modem diagnostic commands include: 

ATi6    Shows retrains, final rx/tx speed, errors and last-call stats
ATi11   Shows modulation, rx/tx levels, snr & V.90 status line/impairments detected
ATy11   Determine if you have a 56k-compatible line
ATi7    Model, Serial #, Product ID/firmware/DSP version
ATi3    Firmware version / modem name

Additionally, 3Com/USR modems will display 'help' for ALL supported commands with this command:

AT $ &$ S$ D$

Later firmware versions may support the AT#UD unimodem diagnostic command.

Lucent/Agere modem i11 displays will tell you about errors, retrains, initial and final transmit and receive rates. ATi3 will tell you your firmware/driver version. See the LT Diagnostics. Later versions may support the AT#UD unimodem diagnostic command.

Rockwell/Conexant hardware modems (ACF) AT&V1 will tell you the initial and final transmit and receive rates, and retrains. The "line quality" is of no value in troubleshooting. AT&V2 will indicates levels and errors. [The information displayed will depend upon firmware version flashed to modem; later firmware also supports AT#UG and AT#UD commands.]

Rockwell/Conexant HCF and Soft56
modems give more information (AT#UG) - see HCF AT#UG. Later versions may also support AT#UD commands (Microsoft's attempt to get standard diagnostic reporting from modems to Windows.)

Note: Some of the output of the &V2 and #UD commands may be encoded - ie:

BEGINaa14ab14ac14ad14ba47bb44bc48bd44cc242END

 Stanislav V. Mekhanoshin's freeware AT#UD and AT&V decoder utilities are available from Modemsite's Download Area.

This is AT &v1 from a Rockwell (Zoom) modem:

at &v1

TERMINATION REASON.......... NONE
LAST TX rate................ 26400 BPS
HIGHEST TX rate............. 26400 BPS
LAST RX rate................ 42667 BPS
HIGHEST RX rate............. 42667 BPS
PROTOCOL.................... LAPM
COMPRESSION................. V42Bis
Line QUALITY................ 024
Rx LEVEL.................... 015
Highest Rx State............ 67
Highest TX State............ 67
EQM Sum..................... 00D8
Min Distance................ 0000
RBS Pattern................. 21
Rate Drop................... 01
Digital Loss................ 2D6A
Local Rtrn Count............ 00
Remote Rtrn Count........... 00
Flex fail

If you have a Cirrus Logic chipset, see the Links page for the Cirrus guide from Jaton's website.

PC-TEL: PCTel modems support the AT#UD and AT#UG modem diagnostic commands. However, this information is lost after the modem disconnects - even if the modem isn't given a reset by Windows. You can make test calls with Hyperterminal, and examine diagnostics while still online; or, see the PCTel page for a trick to get diagnostic information on DUNs calls.

Microsoft's Unimodem Diagnostics Command - AT#UD

Microsoft's attempt to provide a standardized reporting of modem diagnostics to Windows applications.

Much of the information reported by AT#UD is in coded form. You can decode it using the Microsoft specification manually. Stanislav V. Mekhanoshin has created a freeware AT#UD decoder utility - available for download from Modemsite, or, with Windows 2000 & XP, you can automate logging of decoded diagnostic information.

The complete specification (in RTF format) available from this Microsoft page.

While many modems support the Microsoft Unimodem Diagnostic Command - AT#UD - and while Windows 2000, XP and Vista support automatic logging of these reports after hangup, most .inf files aren't supplied with the correct values for this feature which results in either no diagnostic report, or one that contains unrecognized responses (garbage). This can be fixed by modifying the modem's .inf file and re-installing the modem. This information is based upon Franc Zabkar's comp.dcom.modems post Subject: Unimodem Diagnostics & Windows 2000/XP modemlog:

To modify the INF file, add the following entries in the section with entries starting with HKR, Responses:

HKR, Responses, "DIAG ", 1, 9e, 00, 00,00,00,00, 00,00,00,00
HKR, Responses, "<cr><lf>DIAG ", 1, 9e, 00, 00,00,00,00, 00,00,00,00

Also edit the Properties key if necessary by setting bit 11 of the 6th double word to 1, as in the following example.

Original:
HKR,, Properties, 1,
80,01,00,00, FF,00,00,00, FF,00,00,00, 07,00,00,00, 0F,00,00,00, F7,07,00,00, 00,C2,01,00, C0,DA,00,00


Modified:
HKR,, Properties, 1,
80,01,00,00, FF,00,00,00, FF,00,00,00,07,00,00,00, 0F,00,00,00, F7,0F,00,00, 00,C2,01,00, C0,DA,00,00


In the original key the 1st double word is "80,01,00,00", and the 6th is "F7,07,00,00".

Bit 11 is identified by converting the second hex-digit pair to a binary value. If bit 11 is not 1, change it to 1, and reconvert the binary value to hexadecimal.

                F7,07,00,00 
                  
                0000 0111
                       ^
                    bit 11

After these changes are made, and the modem is reinstalled, the modemlog will produce a list of correctly parsed DIAG responses together with a decoded diagnostic report.

PC Tel: The modem may support the #UD command, but not have valid data after DUNs. The PCTel page has information and a workaround.

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