This is a Frequently Asked Questions list about Device::Modem perl extension.

What is Device::Modem?

Device::Modem is a perl extension written in pure perl that allows to communicate with modems, or generically with AT command set compliant devices connected to your computer via a serial port.

Who is the author of this work?

Cosimo Streppone (, an Italian guy, who works and enjoys writing perl programs and objects. If you want to know more, go to

BTW, what is Perl?

If you are asking that, probably you are in the wrong place.

Perl is a wonderful programming language, that cuts development times, helps developer keep mental health, good life-style, doesn't pollute developer's mind, allows complete freedom of style, and (from perl manual), gives you enough rope to hang yourself.

Some starting points:

What is an AT command set?

It is a set of standard commands, also called Hayes, in which (almost) all commands begin with AT prefix and they allow to control a modem, router, whatever device. Also cellular phones work with a subset of standard AT commands.

What is a modem?

What the heck are you doing here?

What are the requisites of Device::Modem?

You must have:

  • A working computer with a standard RS-232 serial port

  • An AT-compliant device (a modem will do perfectly here :-)

  • A working Perl installation

  • Device::SerialPort module installed if you are on some unix platform. Win32::SerialPort module installed if you are on Win32 platform.

Is it multi-platform?

Device::Modem works close to the serial port communication layer, which varies on many platforms. It relies on Device::SerialPort and Win32::SerialPort modules for all low-level communication layer.

It tries to build a platform independent layer above these two low-level modules, so developers don't need to distinguish among different platforms.

It's been reported to work on Win32, Linux, Mac OS X, FreeBSD, NetBSD, OpenBSD, ARM-Linux and Solaris.

Can I use it for my commercial application?

Yes, it is allowed by its license, that is the same as Perl language. If you are using it in a commercial package, or plan to do so, please inform the author (Cosimo Streppone, Thank you.

Why the [insert_you_preferred_feature_here] does not work?

This is an open-source software developed in my little home spare time and for my personal interest and amusement. This module has a test suite, but it is not very extensive, so it is possible that some feature X does not work, or it is not implemented yet or I cannot test it.

If you are in this situation, please contact me and provide the following information:

  • Your operating system version and architecture. Complete output of perl -V command is good for this.

  • Your perl version. Again perl -V.

  • Your Device::Modem, Device::SerialPort and (if you are using it) Device::Gsm version. In case of doubt, send the output of:

            perl -MDevice::Modem -le 'print Device::Modem->VERSION'

Thank you.

Do XModem transfers work?

This is definitely reported to be working by several users, who also contributed patches and tested the feature.

Otherwise, just look at Aaron Mitti's Device::SerialPort::Xmodem CPAN module.

XModem sucks. What about ZModem?

It might seem that XModem and ZModem should be well over dead at this point. But, looks like several old/new devices still support them.

So, ZModem support has been contributed by a user, and will be added to the main release Soon(tm).

Why I keep getting "can't open device: /dev/xxxxx at .../ line 468" errors ?

First of all, be sure to use Device::Modem version 1.52+.

Probably you don't have the correct permissions to access your modem device (usually /dev/modem, or /dev/ttyS0 on unix and COM1/COM2/... on windows). Or you are trying to use the examples that come with Device::Modem distribution with an older version (Device::Modem <= 1.33).

In this case, you should upgrade to Device::Modem 1.52+.

Why I get the error "Can't call method "purge_all" on an undefined value at .../ line 545" ?

Again, upgrade to Device::Modem version 1.52+.

If you get this error, it means that the communication port could not be opened. Most probably you don't have permissions to access your serial port, or you have used a wrong device name (check your device entry in /dev folder).

Since version 1.52, Device::Modem::connect() will try to automatically reconnect if your port connection shuts down, or the Device::SerialPort, or Win32::SerialPort underlying object is deleted or invalidated.

You should really upgrade to Device::Modem 1.52+.

Can I make voice calls with this modem?

No. What you can do, is voice call dialing. After the dialing though, you have to speak. Your computer can not do that, unless you have a PBX board, at least not with Device::Modem.

This module is pretty slow. What can I do?

Make sure you are using that latest version. From version 1.30, the main "send-command" / "wait-answer" cycle has been sensibly improved for speed, though you now have to specify a timeout if you want the module to wait an answer if modem is not ready.

Probably this is the better compromise...

Can I make a [insert_your_preferred_number_here] euro donation to you for this fantastic module?

Oh, yes! Please feel free to contact to decide details about this... :-)

Or, if you have nothing wrong with that, go to my Amazon wishlist.

I think you are a ?#!x$*z!#(!* and your software sucks


Please contact me, so I can improve my software design, ideas and coding, but only if you explain the reasons of your criticism. Thank you.