Terminal FAQ

Terminal FAQ Table of Contents

What is a terminal ?
VT100? TTY?

What is terminal?

A terminal is basically a remote access point. Way back in the early days of computing there were mainframes that did the actual work, and a sprinkling of terminals that accessed the massive computing power of the mainframe. Over the years, mainframes kind of lost their attractiveness, and were replaced by PCs at the workstation. Those old mainframe programs still did useful stuff though, and many were ported to work on regular PCs, but still maintained their terminal support. Nowadays, a true terminal is a pretty rare thing to find, instead PCs are running terminal emulators. These terminal emulators, er, well, they emulate the traditional terminal.

In APRO, a terminal is used to emulate a VT100 or TTY terminal. Probably the most common use is to use the TAdTerminal component to interactively communicate with a serial device. Drop a TApdComPort and a TAdTerminal on a form and run it, and you'll have a handy terminal program where you can send commands to a modem or other device. Received characters are automatically displayed in the terminal window, and key-presses in the terminal window are sent out the port to the device. Pretty handy, eh?

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VT100? TTY?

The mainframes of yesteryear came in several different flavors, each with it's own terminal to connect to it. Each terminal, in turn, had it's own set of commands to do things like change text color, change fonts, move the cursor, etc. The APRO terminal can emulate the VT100 and TTY terminals with ready-to-use components. Dropping a TAdTerminal on the form will create an internal TTY emulator, to select VT100 emulation, drop a TAdVT100Emulator component on the form as well. To switch back and forth between TTY and VT100, drop a TAdTTYEmulator on the form and change the Emulation property to point to the desired emulation.

TTY is a very basic emulation. TTY (TeleTYpe) doesn't do much, other than display the characters as they are received/entered. You won't find anything related to font colors in TTY, consider it similar to the old Windows Notepad, nothing fancy. The abundance of nothing fancy makes it easy to read, easy to configure, and it has very low overhead.

VT100 is a more advanced emulation, the terminal server (the "mainframe") can control the cursor position, font/background color, etc. There are even a few graphics modes. VT100 also supports VT52 and a few minor variations. The thing to remember about the VTXxx emulators is that they are supposed to get their information concerning screen layout from the terminal server, so don't be surprised if your custom green on red terminal changes to black and white.

If TTY or VT100 don't suit your needs, you can always create your own custom terminal emulation. Your best source of information is the existing TTY and VT100 emulation source code.