On 20 Jun 2006 17:26:02 -0700, put finger to keyboard
and composed:

Franc, the USR 56K Faxmodem is also an internal soft modem (new
word?).

Modems are classified as "soft", controllerless, or "hard". The former
has a DAA and not much else, the second has a DAA + DSP, and the
latter has a DAA + DSP + controller. If any functional block is
missing, then it is emulated by a driver. Softmodems are technically
the worst because they rely on the host CPU to do everything. That is
not to say that softmodems are necessarily bad.

All of today's modems have setup switch settings, either hard or soft.

Some external USR modems, eg Courier, had a physical bank of switches.
I thought you were referring to them.

Without these the modem would be relatively inflexible and useless.
It's usually the modem initialization control command that sets them
up, and they typically run from S1 to S7 or more. These determine such
basic things such as if the modem is on-line continuously, normally
off-line, auto-answer, automatic retries, etc. You need to have a copy
of the chipset producer's technical data sheet to learn how to use
them, without which the chipset is virtually useless.

I know of no S-register that would cause a modem to power up in an
off-hook state, nor any reason why you would want it to. If the
software or the modem's driver is commanding it to go off-hook, then
something is very wrong. Having said that, I seem to recall some
Conexant modems that would not release the line after disconnection.
The fix was a driver update.

If you are a Windows user, your modemlog file will tell you which
commands are being sent to your modem, and how the modem is
responding.

Without knowledge of what these settings mean and how to use them,
you're simply flying blind. This is why you need the data sheet.

An ATZ command will reset the modem and an ATH will hang it up. Both
commands are normally sent by DUN in the course of a dial-up session.
I'd suggest that the OP launch a HyperTerminal comms session and send
an ATE1M2L3 command (to enable command echo and turn on the speaker at
max volume) and then send an ATH1 to take the modem off-hook and an
ATH to hang it up. Monitor the voltage at the wall outlet while doing
this. The on-hook voltage should be about 50V and the off-hook volts
should drop to around 10V-20V.

It may also be interesting to see whether the modem is able to pulse
dial, eg ATDP12345678, as this relies on interrupting the loop current
via the hook switch.

When you purchase an integrated system, the system designers have
already done this basic bit of homework for you.

The factory settings are restored by an AT&F command.

But if you're starting
with the raw chipset, you have to do this bit of research for youself.

Harry C.

I found these documents useful:

"Software Modem and Audio/Modem Riser (AMR) Design"
http://www.eetasia.com/ARTICLES/1999...TEK_CT_TAC.PDF

Modem user manual with a chapter on SM56 AT commands:
http://www.modem-help.freeserve.co.u...la_sm56pci.pdf

- Franc Zabkar
--
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