Modem Init Strings
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Click here for beginner-level instructions on
how to make Doom2 connect using two modems.

The quality of Doom2 modem to modem gameplay, even when run on modern P3 class machines, tends to be enhanced by using an init string that causes the modems to connect without compression, error correction, and sometimes certain kinds of flow control. This likely is due to latency caused by some modems while they perform these operations on the packets. This relatively slight latency, while it does not seem to disturb Windows games and terminal applications, can cause a stuttering or slower game in modem to modem doom2.exe.

Doom2 uses a file named modem.cfg to tell it how to talk to the modem. The three important lines of the file are:

Line 1: modem init string

Line 2: hangup string (a common one is +++ath or just ath, the game will run ok if this is wrong)

Line 3: baud rate (common rate is 19200, supposedly going higher than this is not beneficial).

Line 4 is a text description of the modem and is unneeded by doom2.exe.

The ideal way to create an init string is to know what kind of modem you have, have documentation for it, and be able to build your init string using the commands that turn off error correction, compression, and experiment with the flow control settings.

Another way is to know at least approximately what kind of modem you have, reference a list of init strings that someone else has put together, and try a few that seem to match your modem type. I have such a list compiled in the second half of this page.

A third way is to run a program that will experimentally probe your modem, and figure out an init string for you. An old BBS software named Apcidoom does this. You can download Apcidoom here, and here is what you need to know to make it create an init string for you:

First, take note of what COM port your modem is configured to use.

Shut your computer all the way down into DOSmode, using start/shutdown/restart in MS-DOS mode. Unfortunately, apcidoom forces you to go all the way down into DOSmode like this, even though we don't need it for what we're doing.

From DOS, and ideally with mouse drivers loaded and working, run the apcidoom setup program, apcidm56.exe. It will prompt you for what directories to install to, etc. It is an old program so the installer is a little clunky.

As part of the installation, it will prompt you for BBS like things, such as your BBS handle, etc. Put in whatever you want, and should it complain that your paths to your game directories are not correct, have the software continue the installation regardless.

At some point in the installation, you will see a screen where it asks you for modem information. This screen has COM port settings on the left, put your correct COM port there. Then click the button on the right labeled "Init Strings". This will bring up a new screen, and a button will be available that says "attempt autodetect".

If the autodetection is successful, it will bring you back to a screen, and where there was an empty box before there will be some of the characters of an init string. It's important to note that the box is usually not big enough to hold the entire init string, and to see all of the characters, you will need to highlight the init string with your mouse and drag the highlighting from left to right.

Write down your new init string, and you are done! Quit out of Apcidoom in whatever way seems easiest.

If you want to go back later and redetect your init string, you would run apcidoom and click File - Apcilink to get back to the window with the COM port and Init Strings button.

Modem INIT string list -- compiled partially from APCIDOOM list. Some modem types have more than one init string listed that could be tried.

A number of newer modems not listed here are based on chipsets that were used in these modems. You can experiment with these init strings on unlisted modems and have a good chance of finding a match.

AT&T: at&fx4&c1&d2\q0%c0"h0\n0
          : at&fx4&c1&d2\q0%c0\n0

Boca Modem V. Fast Class:  at&fx4&c1&d2&k0&q0s46=136
Boca Modem - other: at&fx4&c1&d2&k0s46=136

Cardinal: at&fx4&c1&d2&k0%c0\n0

Codex: at&fx4&c1&d2*fl0*sm0*dc0

Com1 MV216 at&fx4&c1&d2\q0%c0\n0

Comcom Spirit: at&fx4&c1&d2*f0*e0

Compaq: at&fx4&c1&d2\q0\n0%c0

Creatix: at&fx4&c1&d2&k0\n0%c0

CTK Shorty: at&fx4&c1&d2*lr0*lg0*m1*e0

Data Flex: at&fx4&c1&d2&k0%c0\n0

Digicom: at&fx4&c1&d2*f0*e0

Dr. Neuhaus: at&fx4&c1&d2\n0\q0

Dynalink: at&fx4&c1&d2&k0%c0\n0

Elsa: at&fx4&c1&d2\q0\n0%c0
      : at&fx4&c1&d2\k0\n0%c0
      : at&fx4&c1&d2\q0\n0

E-Tech: at&fx4&c1&d2$f5$c0$e0

Gateway: at&fx4&c1&d2&k0\n0%c0
             : at&fx4&c1&d2&h0&r1&k0&m0
             : at&fx4&c1&d2\q0\n0%c0

GVC: at&fx4&c1&d2\q0%c0\n0

Hayes: at&fx4&c1&d2&k0&q0S46=136

Hidem: at&fx4&c1&d2\q0%c0\n0

Holmes: at&fx4&c1&d2&k0%c0\n0

Infotel: at&fx4&c1&d2&k0&q0s24=136

Intel: at&fx4&c1&d2&k0\n0%c0
      : at&fx4&c1&d2\q0%c0"h0\n0

KE Worldblazer: at&fx4&c1&d2S58=0s68=255s190=0s180=0

Kingston: at&fx4&c1&d2&k0\n0%c0

Kortex: at&fx4&c1&d2&k0&c0/n0/g1

Lasat: at&fx4&c1&d2&k0&c0/n0/

LightFax: at&fx4&c1&d2&k0&c0/n0/

Logem: at&fx4&c1&d2\q0%c0\n0

M. Bullet: at&fx4&c1&d2$m5$c0$e0

M. (other): at&fx4&c1&d2&k0%&c0\n1

Maestro: at&fx4&c1&d2&k0\n0%c0

Megahertz: at&fx4&c1&d2&k0&q0s46=136
                : at&fx4&c1&d2\q0\n0%c0
                : at&fx4&c1&d2&q0\n0%c0
                : at&fx4&c1&d2&k0\n0%c0

Microm: at&fx4&c1&d2\n0\q0%c0
            : at&fx4&c1&d2\n0&k0%c0

Microgate: at&fx4&c1&d2&k3&q5%c0

Motorola: at&fx4&c1&d2\q0%c0\n0

Multitech: at&fx4&c1&d2&e3&e1&e14&e0

NEC: at&fx4&c1&d2\q0%c0\n0

Octocom: at&fx4&c1&d2&k0&e0*e0

Piel: at&fx4&c1&d2&k0%c0\n0\g1

Practical Peripherals: at&fx4&c1&d2&k0&q0S46=0
                               : at&fx4&c1&d2&q6&k0&q0s46=0
                               : AT &F V1 &C1 &D2 X4 &K0 &Q6 S11=50 S46=136

Racal RMD: at&fx4&c1&d2&k0%c0\n0
                  : at&fx4&c1&d2\q0\m1\c4\n0
                  : at&fx4&c1&d2&k3%c0\n0

SAT: at&fx4&c1&d2&k0%c0\n0

SBN: at&fx4&c1&d2\q0%c0\n0

Smartlink: at&fx4&c1&d2&k0%c0\n0

Supra: at&fx4&c1&d2&k0%c0\n0

Sysnet: at&fx4&c1&d2&k0\n0%c0

Telebit: at&fx4&c1&d2s58=0s68=255s190=0s180=0

Telejet: at&fx4&c1&d2&k0\n0%c0

Telelink: at&fx4&c1&d2&k0\n0%c0

Tornado: at&fx4&c1&d2\q0%c0\n0

UDS Motorola: at&fx4&c1&d2\q0%c0\n0

UFOMate: at&fx4&c1&d2$f5$c0$e0

US Robotics: at&fx4&c1&d2&r1&h0&k0&m0

US Robotics Sportster 56000 Voice Internal: AT &F V1 &C1 &D2 X4 &K0 S11=50 S46=136

Ven-Tel: at&fx4&c1&d2%f0%c0\n0
            : at&fx4&c1&d2&k0%c0&q0

Western Datacom: at&fx4&c1&d2&k0&c0\n0

Zoom: at&fx4&c1&d2&k0%c0\n0
         : at&fx4&c1&d2&k0%c0&q0

Zytel: at&fx4&c1&d2&h0&k0