Zoom 144 modems - Many have Rockwell chips that do not have error correction (most, not all Zoom 14.4 modems). Some have standard RPI, others have RPI+. One way to tell which you have is from reading the box or supplied manuals. Another is by issuing ATI3 to the modem while in a terminal program.

For more information, See The Rockwell Personal Notes

This is a note that I received from an Internet user on 3/28/97 concerning a Zoom V.34 modem...


As a last resort to the very picky nature of ZOOM modems, when all else fails, and you think it is defective, try this in your init string.
AT%C0S48=0
Yeah, I know. It disables compression. So what. Most files are already compressed anyway. But this is the only way I can get mine to stay online.

This is a note that I received from an Internet user on 12/26/97 concerning a Zoom V.34i model 2805 modem...

Think I've got a solution for you to post. Had a long-running battle with
the above, in which it would "choke up" and act like it was disconnected
when, actually, it was still hot: it just wasn't accepting information --
in EITHER direction.

Zoom has finally submitted a string that seems to work. It is:
AT&F&Q5%C1S7=100S10=100&C1&D2

I have absolutely no idea what it's telling the modem but, whatever it is,
it works.