Now that you’ve had a chance to play with a standalone VT100 Terminal, not to mention Dual VT100 Terminals, it’s time to take PCjs Machines to the next level, and begin connecting PCs to terminals.

Below you’ll find an 80286-based IBM PC AT connected to an 8080-based VT100 Terminal via the PC’s COM2 serial port.

At this point, the connection is very thin. The PCx86 SerialPort and PC8080 SerialPort each export exactly two methods:

  • initConnection()
  • receiveData()

The receiveData() method always returns success, because both SerialPort components buffer all received data. For now, the VT100 SerialPort component avoids overflowing the VT100 firmware’s buffers by automatically throttling the flow of data whenever the firmware, in desperation, issues an XOFF. This “Auto XOFF” behavior will eventually be superseded by additional interfaces that provide conventional RS-232 signal-based flow control.

What can you do with these machines? Click on the PC screen and type:

DIR > COM2

or any command redirected to COM2. The output should appear on the VT100’s screen.

A more interesting example:

CTTY COM2

redirects all stdout (screen) and stdin (keyboard) I/O to the VT100. Then click on the VT100 screen to switch focus, and you can now interact with the PC via the terminal. The CTTY CON command will restore control to the PC.

More useful scenarios include machines running PC-based debuggers that communicate via a serial port, such as the OS/2 kernel debugger, Windows debuggers like WDEB386, some versions of SYMDEB, and so on. PC-to-PC configurations will also be possible, enabling live demonstrations of classic communication software packages such as CROSSTALK.

I’ve also made it incredibly easy to put machines like this on any PCjs web page. For this blog post, all I had to do was add the following Front Matter to the top of the Markdown file:

machines:
  - id: ibm5170
    type: pcx86
    connection: com2->vt100.serialPort
    config: /devices/pcx86/machine/5170/ega/2048kb/rev3/machine.xml
  - id: vt100
    type: pc8080
    connection: serialPort->ibm5170.com2
    config: /devices/pc8080/machine/vt100/machine.xml

and then embed the machines in the post, each with a single line:

{% include machine.html id="ibm5170" %}
{% include machine.html id="vt100" %}

For people rolling their own web pages, the basics haven’t changed, and adding a serial connection merely requires adding a connection property (eg, connection:"com2->vt100.serialPort") to the parms parameter passed to the embedPCx86() interface. A similar property (eg, connection:"serialPort->ibm5170.com2") must also be added to the parms passed to embedPC8080().

For the more adventurous, a Dual Debugger Configuration is also available.

[PCx86 Machine]

[PC8080 Machine]

@jeffpar
Aug 19, 2016