Ethernet Gateway

The gateway's serial ports emulate a Hayes Smartmodem. A vintage computer drives them with the same AT commands it would send a real modem — except a “dial” opens a TCP connection instead of a phone call.

Each of the two serial ports, when in Modem (AT Command) Mode, presents a Hayes-compatible command interface. Your retro machine's terminal program talks to it exactly as if it were a Smartmodem 2400 or compatible: type AT commands in command mode, “dial” to open a connection, exchange data in online mode, and use the +++ escape to slip back to command mode without dropping the link. There is no phone line — ATDT host:port is a TcpStream::connect().

• Every command line begins with the attention prefix AT (or at — commands are case-insensitive) and ends with a carriage return.
• The lone exception is A/, which repeats the last command with no AT and no carriage return.
• The modem answers with a result code — OK, CONNECT, ERROR, etc. — in words (verbose) or as a digit (numeric), controlled by ATV.
• Several commands can be chained on one line (ATE0Q0V1); see Command Chaining.
• Numeric command parameters default to 0 when omitted: ATH = ATH0, ATE = ATE0.
• Settings are held in RAM; AT&W persists them to egateway.conf and ATZ reloads that saved profile.

The ATIn family reports product and firmware strings — some terminal programs probe these to recognise the modem.

In verbose mode the modem returns the word; in numeric mode (ATV0) the digit. Which codes can appear depends on the ATX level (below).

A gateway-specific vendor extension that makes ASCII BBSes readable on a PETSCII Commodore when you dial them directly over TCP.

With AT+PETSCII=1, on a direct-TCP dial the emulator:

• Case-swaps letters in both directions, because a C64 in upper/graphics mode maps the cases opposite to ASCII — so an ASCII BBS like telehack.com reads in the right case.
• Maps ASCII Backspace ↔ PETSCII Delete (0x14) so the C64 INST/DEL key edits correctly, including while you type the AT command line itself.
• Strips inbound ANSI escape sequences (ESC [ … cursor / colour codes) so they don't spray as garbage on a screen that can't render them.
• Normalizes punctuation the C64 can't show: the back-tick and UTF-8 “smart” single quotes fold to ', smart double quotes to ", tilde / en- / em-dashes to -, the ellipsis to ...; other undisplayable high bytes are dropped or shown as ?.

A “dial” is a TCP connect. The dial string is a host:port, a stored slot, or a phone number mapped in dialup.conf.

Honoured only when the dial string looks like a phone number (digits + formatting). A hostname such as pine.example.com is dialled verbatim — modifiers are not stripped from it (except a trailing ;).

S-registers hold numeric timing and behaviour parameters. Query with ATSn?, set with ATSn=v (0–255), list help with ATS?. AT&W saves all 27; ATZ restores them; AT&F resets to factory.

How to get back to command mode without hanging up.

While online (passing data), typing +++ framed by a guard time of silence on both sides drops you to command mode with the connection still alive. From there, ATO resumes the data session and ATH hangs up. This is the exact Hayes guard-time behaviour:

• The escape character is S2 (default 43 = +).
• The guard time is S12 / 50 seconds (default S12 = 50 → 1.0 s) of silence required both before the first + and after the third.
• Setting S12 = 0, or S2 > 127, disables escape detection entirely.
• Exactly three escape characters are required — fewer or more pass through as data.
• Any non-escape byte sent in the middle cancels the sequence (it's treated as data).

(online, exchanging data)
   ...wait ~1 second of silence...
+++
   ...wait ~1 second of silence...
OK                       now in command mode, link preserved
ATO                      resume the data session
   -- or --
ATH                      hang up for good

Multiple commands can ride on a single AT line, the way real Hayes modems accept init strings. The emulator parses left-to-right, applies each subcommand, and emits a single OK at the end (or ERROR at the first failure — subcommands before the failure still apply; those after do not run). Spaces between subcommands are tolerated.

Some subcommands terminate the chain because they consume the rest of the line or leave command mode:

• D… — any dial command goes online and consumes the rest of the line.
• A — answer; leaves command mode.
• O / O0 — return to online mode.
• &Zn=… — the stored-number value runs to end of line.

S-register set values stop at the first non-digit, so ATS0=2E0 sets S0=2 then turns echo off — no separator needed.

Common things you'll actually type. Lines without a result code shown assume verbose mode (the default).

AT                       OK
ATDT bbs.example.com:23
CONNECT 9600
(you're online — the BBS appears)

ATDT ethernet-gateway
CONNECT 9600
(the Ethernet Gateway main menu appears)

AT&Z0=bbs.example.com:23   OK
AT&W                        OK   (persist it)
ATDS0                       CONNECT 9600

ATE0Q0V1X4               OK
(echo off, result codes on, verbose, full extended codes)

+++                      OK   (still connected)
ATO                      CONNECT 9600   (back online)
...or...
ATH                      NO CARRIER   (hung up)

ATS0=2                   OK   (auto-answer after 2 rings)
ATS7=50                  OK   (wait up to 50s for a slow connect)
ATS0?                    002  (query: 3-digit decimal)
AT&W                     OK   (persist)

AT+PETSCII=1             OK   (translate ASCII ↔ PETSCII)
ATDT telehack.com:23
CONNECT 9600
(text now reads in the correct case on the C64)

ATDT bbs.example.com:23
NO CARRIER   (busy — try again)
A/                       (repeats the dial, no AT/Enter needed)

Deep-dive reference pages for every protocol and interface, plus the character-set tables and ANSI escape-sequence reference.