{"id":957,"date":"2020-06-15T09:54:00","date_gmt":"2020-06-15T16:54:00","guid":{"rendered":"https:\/\/www.weinstein.org\/blog\/?p=957"},"modified":"2020-06-07T11:20:05","modified_gmt":"2020-06-07T18:20:05","slug":"ye-olde-tyme-apple-hacking-serial-connection","status":"publish","type":"post","link":"https:\/\/www.weinstein.org\/blog\/index.php\/2020\/06\/ye-olde-tyme-apple-hacking-serial-connection.html","title":{"rendered":"Ye Olde Tyme Apple Hacking: Serial Connection"},"content":{"rendered":"\n

In a previous post, Ye Olde Tyme Apple Hacking<\/a>, I outlined hardware modifications I recently made to a Macintosh LC. Naturally, this brought me in mind of a \u201chack\u201d I wrote up years ago in Apple Hacking for Fun and Profit<\/a> that outlined how I connected an Apple \/\/c to a Mac Mini to use the \/\/c as a serial terminal.<\/p>\n\n\n\n

Since a serial connection and terminal software was also standard fare for classic Macs, I decided to revisit my pervious setup with my Mac LC and a modern-day (2017) iMac.<\/p>\n\n\n\n

 <\/p>\n\n\n\n

Initial Setup<\/strong><\/h2>\n\n\n\n

With regards to hardware, the cabling remains mostly unchanged, a USB to Serial adaptor<\/a>, a null modem<\/a> and a serial cable. The only notable difference is that the LC\u2019s two serial ports (labeled Printer and Modem) are mini-DIN<\/a> connectors whereas the \/\/c used the larger format DIN connector<\/a>.<\/p>\n\n\n\n

\"\"
USB to Serial Adaptor<\/em><\/figcaption><\/figure><\/div>\n\n\n\n
\"\"
RS-232 Null Modem<\/figcaption><\/figure><\/div>\n\n\n\n
\"\"
min-DIN to RS-232 Cable<\/em><\/figcaption><\/figure><\/div>\n\n\n\n

For terminal emulation on the Mac LC, I went with ZTerm<\/a>. ZTerm<\/strong> was a shareware terminal emulator for the Mac originally introduced for System 7<\/a>. <\/p>\n\n\n\n

On the iMac, I\u2019m running macOS 10.15 (Catalina<\/a>) which will only run 64bit applications. I note this because I’m reusing my Keyspan USB to Serial adaptor from 2007 and the software installer for the drivers of the chipset in my adaptor<\/a> haven’t been updated to run in a 64bit-only computing environment. I was able to solve this apparent impasse by downloading and running Serial 2<\/a>. Serial<\/strong> was able to recognize and install the proper drivers on the iMac without issue.<\/p>\n\n\n\n

In fact, I would recommend purchasing Serial<\/strong> for a couple of reasons, beyond getting out of this pinch. First, with Serial<\/strong> running on the iMac and ZTerm<\/strong> on the LC, it\u2019s a simple matter of typing in a few keys to confirm the serial connection is in working order. Secondly, which I\u2019ll go into detail in the second part of this post, Serial<\/strong> pairs well with ZTerm<\/strong> in supporting older file transmission protocols such as Kermit<\/a> and ZModem<\/a>, thus enabling the transfer of files between the two systems.<\/p>\n\n\n\n

 <\/p>\n\n\n\n

Perfecting getty<\/strong><\/h2>\n\n\n\n

The one thing that always bugged me about my old hack was the use of gnu screen<\/strong><\/a> to initialize the terminal session. The proper setup should be that the host system listens on the established line for an inbound connection and then initializes the login process when the connection has been established. This is what getty<\/strong><\/a> is for. What I didn\u2019t consider back then was, how will getty<\/strong> be managed? For macOS, the answer is launchd<\/strong><\/a>.<\/p>\n\n\n\n

With that in mind, here are the configuration settings for getty<\/strong> and launchd<\/strong><\/a> on the iMac: <\/p>\n\n\n\n

Modify the file \/etc\/gettytab<\/em> to define a terminal type. For example, append :tt=vt10<\/em>0 to the following line in gettytab<\/em>:<\/p>\n\n\n\n

2|std.9600|9600-baud::np:sp#9600<\/code><\/pre>\n\n\n\n
So now you have something like this:<\/p>\n\n\n\n
2|std.9600|9600-baud:\\\n    :np:sp#9600:tt=vt100:<\/code><\/pre>\n\n\n\n
This will tell getty<\/strong> that a incoming connection labeled std.9600<\/em> should established at 9600 baud<\/a> connection and use the vt100<\/a> terminal settings. <\/p>\n\n\n\n
For launchd<\/strong> create a property list<\/a> (p-list) file in \/Library\/LaunchDaemons<\/em> with the following:<\/p>\n\n\n\n
<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<!DOCTYPE plist PUBLIC \"-\/\/Apple\/\/DTD PLIST 1.0\/\/EN\"\n\"http:\/\/www.apple.com\/DTDs\/PropertyList-1.0.dtd\">\n<plist version=\"1.0\">\n<dict>\n    <key>RunAtLoad<\/key>\n    <true\/>\n    <key>KeepAlive<\/key>\n    <true\/>\n    <key>Label<\/key>\n    <string>serialconsolelc<\/string>\n    <key>ProgramArguments<\/key>\n    <array>\n        <string>\/usr\/libexec\/getty<\/string>\n        <string>std.9600<\/string>\n        <string>tty.USA19H22P1.1<\/string>\n    <\/array>\n<\/dict>\n<\/plist><\/code><\/pre>\n\n\n\n
A few bits about the contents of this file:<\/p>\n\n\n\n