JB> I am trying to understand how to correctly place the
 JB> different parameters that make up an initialisation string
 JB> for a modem.

 JB> Can anyone recommend a book?

No, unfortunately.  There's a file, What You Need To Know About Modems
(WYNTKAM.*, ~37K), well worth a look, but it's not long on Hayes-compatible
modem parameters.

 JB> I have read the manual that can with the modem I have
 JB> borrowed, and whilst it tells me waht each parameter
 JB> means/what it does, I have no idea if it is necessary to
 JB> ensure certain ones go first.

Generally not, unless one changes the settings made by another.  This can
be a problem with Rockwell-based modems, where several different commands
may produce similar results, or override other commands, but ..

 JB> As far as trying to work out an init string for this modem
 JB> (Dataplex 225 V.34) is it just a matter of putting in those
 JB> parameters that it does not default to?

Yes, if you haven't already modified the stored settings with &W, or
you can always start off with &F for factory settings.  Dump your
settings after a &F to print; you may find that some of them differ
from what your manual reckons.

Better still, set it up how you most often want it, store that setting with
&W (or &W1 etc for different profiles) then use ATZ (or ATZ1 etc)
as your primary Init.  You may wish to then set particular parameters for
some program or system you're calling, which you should do after
ATZ has had a little time to settle.  With the notation that |
means , and ~ means a half second delay (varies between comms
progs) then perhaps something like:

ATZ|~~AT

 JB> I find the whole thing confusing!!

Welcome to the club :)  The Dataplex modems tend to use different commands
for the Hayes extended commands than other modems, even Rockwell based
ones, though the DPX225 uses a Rockwell DSP chip, but different firmware.

So, for example if someone suggests %E or &E settings from their
Rockwell, be aware that those commands often will need to be quite
different for the DPX225 (in fact, &E sets error correction, and %E may
adjust the compromise equaliser on some DPX modems.  Maybe Arthur Marsh'll
have details, he had one for ages.

You'll have to work back from what the commands are supposed to do, rather
than what they're called, assuming gaining some familiarity with your
manual.

You may find Maestro's on-line manual (NEW-EXEC.*, ~60K) useful as a
reference for pretty-well bog-standard Rockwell (and subset Hayes)
commands, to compare with yours.  Be aware that many S-register settings
(past the first dozen or so defined by Hayes) will have quite different
functionality, though I think I heard some were the same (like S95 to set
response codes?)

 JB> I was hoping that someone could let me know about a book
 JB> that help one to understand init strings.  Some of the ones
 JB> in Dymocks etc tell you all about how modems work but
 JB> ignore the init string part.

Forget them - they certainly won't help with yours.  Apart from finding
about one or two 'trick' settings, most modems are happy to work with
near-default setup, once you've got it right.

 JB> I'm starting to think it's one of the black arts!!

Oh it is, but there are some helpful devas around ..

Ian

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