This is a complete ASCII VT100 compatible video terminal in a single chip. You can use it as a normal serial terminal with keyboard and display or as a single chip controller to add a video output to a Micromite, PICAXE project or other Single board computer.

It has a serial interface with TTL or RS232 signal levels, input from a standard PS2 style keyboard and output to a VGA or composite monitor. There is also a USB interface which supports serial over USB and acts as a USB-to-serial converter.

The firmware emulates most features of the DEC VT100 and VT52 terminals and has extensions for graphics (lines, boxes and circles) as well as alternative fonts (large and jumbo).

The entire terminal (video generator, serial interface, etc) is contained in a single low cost chip. You can use it to build a complete terminal (as illustrated on the left) or as a single chip video driver, keyboard interface or whatever.

Specifications

• Single chip ASCII video display terminal with VT100 and VT52 emulation
• VGA or Composite Video output with automatic switch over. Composite can be PAL or NTSC.
• VGA can display 24 lines x 80 characters or an extended resolution of 36 lines x 80 characters
• Composite video can display 18 lines x 48 characters (PAL) or 15 lines x 44 characters (NTSC)
• Standard PS2 compatible keyboard input with support for standard US keyboard layout or French, German, Italian, Belgian, Russian or United Kingdom keyboard layouts
• TTL or RS232 serial input/output. Baud rates from 40 to 1,000,000 bits per second with odd, even or no parity and one or two stop bits
• USB input with serial emulation. This can be used as a USB to serial converter
• Extended VT100 terminal emulation. Extensions include graphics codes for drawing lines, boxes and circles (which can be hollow or filled)
• Graphics resolution is 480x288 pixels in VGA 25 line mode, 480x432 pixels in VGA 36 line mode, 288x216 in PAL composite and 264x180 pixels in NTSC composite mode
• Three built in fonts (standard, large and jumbo) and four character attributes (normal, underline, reverse and invisible)
• Power requirement is 5V at 50mA plus any current drawn from the 3.3V pin on the serial connector

Circuit

The ASCII Video Terminal is based on a low cost 32-bit microcontroller from Microchip. Under control of its firmware this chip does almost everything including generating the video, decoding the keyboard, driving the USB, sending/receiving data over the serial interface and running the VT100 emulation. The only other significant component is a three terminal regulator used to provide the 3.3V power to the microcontroller.

you can find images in high resolution copy on project page

The video is generated from separate I/O pins on the microcontroller for the VGA and composite outputs. This enables the signal levels to be optimised to suit the type of display. Note that only one type of monitor should be connected at any one time.

The microcontroller automatically determines the type of terminal that is connected on power up. It does this by measuring the resistance from pin 12 to ground. If it is less than 2K it assumes that a VGA monitor is plugged into the VGA connector and the video should be generated at pin 12 with the correct timing for a VGA monitor. Otherwise the firmware assumes that a composite monitor is connected and the video is then generated from pin 6 with timing to suit the PAL standard (NTSC can be selected on the setup screen).

The remainder of the circuit is reasonably standard and does not need explanation.

check for more info on project page: http://geoffg.net/terminal.html

http://geoffg.net/Images/Terminal/SchematicLarge.png