argv minus one<p>The <a href="https://mastodon.sdf.org/tags/Hayes" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>Hayes</span></a> <a href="https://mastodon.sdf.org/tags/Smartmodem" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>Smartmodem</span></a> had a separate data mode (in which bytes are sent/received over the phone line) and command mode (in which the computer sent commands to the modem itself).</p><p>Switching from command to data mode was simple: send the command `ATO`.</p><p>The reverse was more complicated. The modem would switch from data mode to command mode whenever the computer tried to send the special character sequence `+++`, with a delay before and after the sequence.</p><p>1/</p><p><a href="https://mastodon.sdf.org/tags/RS232" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>RS232</span></a> <a href="https://mastodon.sdf.org/tags/modem" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>modem</span></a> <a href="https://mastodon.sdf.org/tags/retrocomputing" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>retrocomputing</span></a></p>