K56flex modem Mini FAQ

Last updated 23/02/98

In response to many requests, a version of the mini-faq for Rockwell chipset based K56flex modems....


Q: I need to get a good 'Init string' for my K56F modem. Do you know any?

A: Forget about Init strings for the moment. Read the REST of the FAQ, first...


Q: I am having trouble with my modem not displaying the correct connect speeds

A: Make SURE that your modem is using the correct .inf file under Windows 95. Many cheap 'unbranded' modems are shipped without this essential software, relying on the standard W95 .inf files. These, unfortunately, were not properly developed at the time, and do not contain the correct result codes listings for K56f modems operating at the higher speeds.

Two things to check:


Q: I have the right .inf file, now but my modem only connects at 33,600 bps, or even slower.

Check that you are dialling a number to your ISP which is connected to K56f-compatible terminal equipment. For Force9 Internet Ltd., this number is :



Q: Got the right number set, but it's still slow. What else could be wrong?

A: Oh, lots of things. Remember that ALL high-speed modem connections are marginal over 'ordinary' telephone lines. Don't expect 56,000 bps - you'll never see it. (And neither will I.) It DOES seem to be true that, here in the U.K., K56Flex modems are more sensitive to variations in line conditions than some other types. Having said that, here's the list of things to check, in this order....


Q: Nope. All that stuff is ok.

A: Are you sure? Go and check it again...


Q: It's DEFINITELY all right. I even have a separate second line installed, just for the computer!

A: Oh yes? Have a look around your premises, (you might need that torch again) and see if there are any strange grey boxes fixed to the walls. It might say "DACS Unit" or something similar. No? OK - it might be outside, or some distance away... How long ago was the second line installed? Just recently, eh? ...And you live in a large centre of population, do you? Uh-huh....

Ring up your local BT engineering office again and give them the numbers of BOTH lines. Ask them: "Are these lines provided using a multiplexer unit, please?" If the answer is "YES" then say: "Well would you mind coming and taking the b____y thing away and provide me with two INDIVIDUAL exchange lines, please?"

K56Flex and X2 -type modems will NOT operate correctly in the presence of a DACS multiplexer. This is a technical cheat used by BT (and others) to get more local lines installed where there are not enough cable pairs under the street in a given area. It doesn't matter how many OTHER premises in your locality are provided with them - you don't want one!

NOW that you have checked all those things, it's time to look at the modem itself...


Q:What about that init string?

A: Look: shut up about the init string, OK? Except for VERY unusual operating circumstances, your modem should connect reliably at 40-50,000 bps WITHOUT messing about with init strings. Its factory defaults are already set up to do that and, if it cannot because of some other external factor, all the init strings in the world will not cure it.

People seem to think that adjusting the modem operating parameters is some kind of 'magic spell' which will give them fast Internet connection speeds without doing any background work. If you want to read articles like that, there are plenty of them on web sites all over the place. Only trouble is, they're mostly nonsense...


Q: What facilities does my modem provide for checking line quality?

A: Quite a few. Here's how to do it...

Start a normal dial-up session to your ISP. let it run for a good while - read you e-mail, play some QUAKE, whatever... Now, disconnect and do not switch your modem off, or reset it. Start Hyperterminal, or some similar comms terminal program and connect direct to your modem port. That will be COM1 or COM2..

In the terminal window, type in AT <RET>

Your modem should respond:


Issue the command AT&V1 <RET>- you should see an information listing like this:

LAST TX rate................ 26400 BPS
HIGHEST TX rate............. 26400 BPS
LAST RX rate................ 42000 BPS
HIGHEST RX rate............. 42000 BPS
PROTOCOL.................... LAPM
COMPRESSION................. V42Bis
Line QUALITY................ 033
Rx LEVEL.................... 014
Highest Rx State............ 68
Highest TX State............ 67
EQM Sum..................... 00D1
RBS Pattern................. 04
Rate Drop................... 02
Digital Pad................. 6dB
Local Rtrn Count............ 00
Remote Rtrn Count........... 00
V8bis K56Flex 9481814339C2

(If this list does not appear, or is clearly all nulls and zeroes, see note [1] below)

The output "Line QUALITY" is significant. In general terms, the lower this figure is, the better. If < 25 then you SHOULD be already getting consistent speeds. 25-35 is OK, 35-40 is poor and 40+ is hopeless. If this test confirms your suspicions about the reliability of your phone line, you should... guess what?.....

Yup. - Ring BT again

Look also at the 'Digital Pad' line. You don't need to know exactly what a digital pad is - (I'm not too clear on it myself) but each one found in the connection path contributes -3db to the line attenuation. This is not normally a serious problem but too many of these (say > 12db) and you will have problems maintaining a K56f connection.

[1] If AT&V1 reports 'ERROR', then your modem does not support this feature and it serves you right for buying a nasty cheap one. If the info is all zeroes, then Win95 is re-setting your modem after disconnecting, which loses the stored information. You may need a registry hack to prevent this, which is outside the scope of this article.
E-mail me for help with this, if you need it.


Q: My connection speed looks OK but when I'm browsing the web, or downloading files, it seems to go slower and slower. Sometimes the incoming data seems to stop altogether. What could be causing this - it MUST be my ISP's fault, right?

A: Not necessarily. Do the "AT&V1" test again, as above. Now check the fields shown as 'LAST RX rate' and 'HIGHEST RX Rate' These are speeds in bits per second. If there is a big difference between the two, then your modem has been re-negotiating speeds, probably in response to intermittent noise or interference on your 'phone line. If the RX rate has NOT varied by much, then the problem you experience may well be due to general Internet congestion, or (more likely) overload and congestion at the remote host or FTP site - about which little can be done.


Q: I got this init string from one of those 'other' websites. Can you explain what it all means, please?

A: <Sigh> OK then... In order of appearance:-

+MS56,1 -sets the modem into K56flex mode. This SHOULD be the default setting, anyway. Other operating modes are also available.

28000 -sets the 'floor' connect speed. The modem will not connect slower than this speed. If this setting is too high for the line conditions, the modem will not connect at all...

56000,1 -sets the 'ceiling' connect speed. The modem will not attempt to connect faster than this. (But may not even reach this speed.)

%E0 -tells the modem NOT to attempt re-training. K56Flex has a dynamic speed adjustment feature which is superior to the old fashioned retrain sequence, and does not have the same 20- or 30-seconds delay associated with it. I recommend that this setting is left at zero.

S202=32 -is an obscure command which should not affect the operation of the device from day-to-day. If you MUST know, it disables part of the negotiation sequence, where the modem attempts to detect more than one digital-to-analogue conversion along the path from the ISP to your location. (Sorry, but you DID ask ;-) Here in the UK, this should not normally be a problem, but beware: if this feature is disabled and there ARE multiple d-to-a conversions along the line, the modem may attempt to connect in 56k mode, but be unable to do so. This could give the effect of an apparent connection to your ISP, but with no login executed, no network packets passed, etc etc.


...More questions will be added to this FAQ, depending on how frequently asked they are...

FINAL WORD: I am NOT a free tech support service for datacomms devices, especially those whose manufacturers and suppliers do not provide this facility to their customers. Having said that, if any Force9 subscribers are having difficulty, or need advice, I will try (but not guarantee) to help...

Hope you found all this of some use. - PMcM

(MT56000ZDX graphic courtesy of Multitech Inc. All trademarks acknowledged.)

HTML version Paul McMichael 1998


Visitors since 23/6/97        Last updated:23/02/98