VT6 with monitor and keyboard on deskThe Spare Time Gizmos' Video Terminal project is a family of general purpose video display terminals.  They communicate with a host computer using standard RS-232 ASCII communications and accept ANSI standard escape sequences.  The VT terminals use any standard IBM PC compatible VGA display as a monitor and an IBM PC PS/2 style keyboard for input.

The VT family terminals are perfect for use with any computer that requires a serial console, especially those of the classic variety.  It works with the Spare Time Gizmos SBC6120 and Elf 2000 kits, as well as any VAX, PDP-11, S-100, or other vintage machine that you might have.  Since the VT family has near perfect emulation of the DEC VT220 terminal, it works with any vintage software that you might have, including EDT or emacs.

As of this writing there are three members of the Spare Time Gizmos’ VT family.


The VT4 was the original prototype unit.  It is no longer in production, but there are a few out there and they continue to be supported, albeit with reduced functionality, by the firmware.


The VT5 is an enhanced version with two serial ports and support for multiple host sessions.  The VT5 is normally a standalone product and is housed in a small metal enclosure approximately 4” by 5” by 1˝”.


The VT6 is a simplified version with only one serial port.  It consists of a 2.5” by 4” PC board and would normally be mounted inside the enclosure for a larger computer.  This would allow, for example, an older PDP-8 or S-100 computer to use a VGA monitor and PS/2 keyboard for a console terminal.


All of VT family terminal do pretty much everything a VT220 can do, plus several extensions.  Here's just a partial list of the features -


Two independent serial ports for two hosts, or host and printer (VT5 only)


Multiple frame buffers with split screen and paged displays (VT5 only)


A programmable 25th line status display


Menu driven setup mode with settings saved to EEPROM.


Reverse video, underline, dim, bold, blinking, double high and/or double width  character attributes


VT525 escape sequences are supported to set foreground and background colors


Automatic screen saver and power down for VESA DPMI compatible monitors


Supports standard PS/2 104 key PC keyboards


Supports LK250, LK411, LK412 and LK450 keyboards in DEC native mode


Software selectable DTE or DCE configuration (VT5 only)


DEC Multinational, UK National,  DEC Special Graphics, DEC Display Controls and VT52 fonts


Downloadable fonts, optionally saved to EEPROM.


Serial printer port with VT220 printer controls (VT5 only)


VT6 startup screenThe firmware for the VT family is an open source community development effort and a Source Forge project has been set up for the VT firmware at http://vt4.SourceForge.net.  The firmware is written in C and is compiled using the free, open source SDCC compiler.  The other tools we're using are Programmer's Notepad and GNU Make, both of which are also free, open source, tools.  New firmware can be downloaded to VT microprocessor, while it's installed in the terminal, using an ordinary PC and a serial connection to the terminal.  No special programming hardware is required to update the MCU firmware and all the development tools used are free.  Lack of money or equipment shouldn't keep anybody from participating.



VT6 PC boardThe VT family terminals contain two independent microprocessors, a primary “MCU” which does most of the work including generating the video, and a secondary “APU” which interfaces to the PS/2 keyboard and handles other miscellaneous housekeeping tasks.   Some people may raise their eyebrows at the idea of a second CPU, but the part costs approximately $2 and offloads the main CPU firmware (and therefore the firmware programmer!) of any critical timing issues in bit banging the PS/2 serial keyboard protocol.  It’s well worth the investment.

The video generation is done by a combination of hardware and firmware.  The hardware generates the basic horizontal timing, and the firmware is responsible for transferring bytes from the frame buffer to the hardware video shift register, which is then shifted out serially to drive the VGA display.  The VGA bitmap requires approximately 30K bytes of RAM, which is far more than the internal memory of the microprocessor, so all VT models provide for 128K or 512K bytes of external SRAM.  Since the maximum address space of the MCU is 64K bytes, the hardware implements a simple memory management scheme to extend the addressing abilities of the MCU.


With lots of memory and approximately a 30MIPs processor at our disposal, there's a lot more that could be done with the VT terminals beyond simply emulating a VT220.  Here's just a few of the ideas that have been discussed -

bulletAdd support for other emulations, such as ADM, HP, Televideo, etc.
bulletAdd support for graphics display, such as ReGIS or Tektronix 4006/4010 emulation.
bulletAdd an Ethernet interface and create a telnet or ssh "network terminal".


bulletPlease read the Spare Time Gizmos store policies before ordering.
bulletSales tax must be charged on all shipments to California addresses.
bulletNon-USA customers please select the international shipping option.

Shipping Status

The initial run of VT6 kits has sold out!  A special thanks to all the early adopters that invested in one.  More parts are on order, and you are welcome to place an order for a VT6 kit now, but be aware that it will not ship until approximately May 25th.

The VT5 is still under development and should be available soon.  The VT4 is no longer being sold.

P/N Description Price
VT User's Manual and Source Code FREE!
VT6-1B VT6 bare PC board only
Etched and drilled, double sided, with solder mask and silk screen.
VT6-PK VT6 Partial Kit w/USA Domestic Shipping
Includes ONLY the PC board, MCU, pre-programmed APU and CPLD
VT6-PK VT6 Partial Kit w/International Shipping
Includes ONLY the PC board, MCU, pre-programmed APU and CPLD
VT6-FK VT6 Full Kit w/USA Domestic Shipping
Click the link above to see a list of all included parts.
VT6-FK VT6 Full Kit w/International Shipping
Click the link above to see a list of all included parts.

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