Blizzard of Zeros:

Emulation Recipes - Atari 800XL / 8 Bit: Telnet to a BBS from the Altirra

Created and Maintained by The Dust Council

Last Update (UTC): 2019-Jul-17

Current Date (UTC): 2020-Apr-05

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Tools required:

A terminal program. Your choice of:


Important Notes:


Install software:


Set up devices to enable modem support

From the System menu, select Devices.

Altirra Devices menu option

Click Add and select 850 Interface Module from the Serial I/O bus devices section. Click OK.

Altirra Devices - 850 Interface Module

For 850 Options, I accepted the defaults which on my system were:

Altirra Devices - 850 Options

Click OK. This will return you to the Devices window.

In the Devices window, select 850 Interface Module and click Add again. Select Modem and click OK.

The following options should be set:

Altirra modem setup

Press OK once you have finished Modem setup Press OK again to get out of the menu



Telnetting to a BBS:

You can drag a disk image into the Altirra window to boot it. For this example, we'll use 850 Express! to connect to an Atari-based board running ATASCII.

You will be presented with a DOS II screen. Select L for BINARY LOAD and enter EXPRS850.COM as the filename. You can also just get a directory using the A command here if you forget the filename. Press Enter to load 850 Express.

DOS II screen: Boot 850 Express!

If you chose to enable incoming connections, you will see a Waiting for connection on port message at the bottom left of the screen.

To set the Baud rate to 2400 (if you set things up to use that speed in the Modem setup screen) use the B key. Because the ATDI sequence to telnet must be in ASCII, we're going to set the mode to ASCII for now using the A key, and will switch to PETSCII once we have executed the connect command.

850 Express! Terminal settings

Press ! to Force Term Mode which will bring you to the terminal screen. F2 will bring you back to the setup screen at any time.

EnterAT and return to ensure that the virtual modem is responding. If so, it should respond OK.

850 Express! - Terminal responding to an AT command

For modems, the most common dial command was ATDT - ATtention Dial Tone. In the early days, there was also ATDP to dial using Pulse. For the purpose of Altirra you want to use ATDI, presumably for Internet. ATDT will not work for telnet.

For this example, we're going to be connecting to 8-Bit Guild, a BBS running BBS Express 850 v1.0, and which supports PETSCII. We're going to execute the connect string, F2 back to the settings menu, use the A key to select PETSCII, then return back to the terminal using the ! command.

The command to connect in Altirra is ATDI port

So for 8-Bit Guild:

ATDI 130

If the board is up, you should see a CONNECT message. At this time you can switch to ATASCII mode.

Connected to BBS

Several of the Atari systems I connected to actually gave you a moment to switch to ATASCII expressly. I normally do it as soon as I connect:

Choose translation

In any event, press F2, then A to select ATASCII. Then press ! to return to the terminal.


Follow instructions to log in.

8-bit Guild Login Screen


Final notes

You may, of course, use ASCII mode to connect to non-Atari/non-PETSCII systems. The process for connecting via other Atari terminal programs is similar. In several cases, F2 also returned to the settings menu. In Altirra, F2 maps to the START key on the original Atari console. Further key mappings can be found in the Altirra help system under How to use -> Keyboard layout.

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