I recently started working on getting my Atari 400 connected to a bbs over telnet/wifi with an esp8266 and wanted to share. I didn't find much about using an esp8266 as a modem with the Atari 8-bits.
I don't have much atari hardware and no SIO cable so, I first made a SIO23v3 breakout. More info on the board at the OSHPark Project page. The idea came from the atari8warez Poor Man's SIO cable and is an edge connector that fits between the two SIO port pin rows. The Data In, Data Out and Command pins are level shifted with mosfets (based off the SparkFun Bi-Directional Level Shifter). This board could also be used for connecting to a Raspberry Pi or other lower voltage device. I'm planning to build another for use with my Zipit Z2 Handheld and sio2bsd.
I have an ESP-01 board that I'm using with this modem emulator. The code is built and uploaded to the esp8266 with the Arduino IDE. The esp8266 is powered by the Atari 5V through a regulator. The command pin is not used at the moment. The ESP-01 is very minimal with few pins but other esp8266 versions have more pins available (can add sd card socket).
The modem software uses AT commands for connecting to access points, speed dial, baud rate, saving settings, etc. I tested both bobterm and icet with the RS232.COM handler and was able to connect to a bbs. The modem also allows incoming connections over telnet which worked from my linux pc. This is the extent of my testing so far and only at 9600 baud.
A couple of other ideas I had (unsure of the feasibility):
- add SIO2Arduino to load the term software and handler
- add SIO2Arduino and sd card; use wifi/webserver on esp8266 to load floppies (plus modem emu?)
- 850 emulation?
Anyhow, as a plain old telnet modem it seems to work well