VT100

VT100 guide

The VT100 was a very popular RS-232 based dumb video terminal introduced by DEC in 1978. It featured cursor keys, and the ability to place text wherever the programs wished onto the screen.

The VT100 was so popular it became THE standard for terminals, and terminal emulators.

The VT100 used an Intel 8080 processor, the later almost identical VT102 used an 8085. VT100 clones (and there were many) would use a number of different processors, not necessarily sticking to the original.

Surprisingly the VT100 could not actually handle 9600 baud full throttle. The serial hardware could, but the screen could not be updated at 960 characters per second. Thus flow control was essential unless working with a slow system (e.g. an old minicomputer..). Xon/Xoff was the most common method for flow control on DEC/VT100 systems. To handle the speed problem some people would put the VT100 into VT52 mode (one of the VT series' features) because VT52 processing had less overhead.[1]

On a personal note, those of us seeing a VT100 for the first time way back then were floored by the "smooth scroll" feature.. now that looked nice. Until you realized how slow it became. Obviously those who demanded speed would turn off the smooth scroll mode and use every other measure to improve how fast the terminal could process data (see above).

Models

• VT100 - 1978 base model.
• VT101 - 1981 cost reduced; no Advanced Video Option (AVO) or Standard Terminal Port (STP).
• VT102 - 1981 cost reduced; built in AVO and STP.
• VT103 - with QBUS backplane.
• VT105 - VT100 with M7071 WG waveform generator board.
• VT110 - VT100 with DPM01 DECdataway Terminal Multiplexer.
• VT125 - VT100 with ReGIS board.
• VT131 - 1982 cost reduced VT132.
• VT132 - VT100 with AVO, STP, and firmware ROMs which support block serial mode.
• VT180 - VT100 with VT18X board, see below.

Options

• VT1XX-AA - 20mA Option.
• VT1XX-AB - Advanced Video Option.
• VT1XX-AC - Serial Printer Interface Option.
• VT1XX-AW - Screen Shield.
• VT1XX-CB - Upgrade kit to convert the VT100 to full VT125 graphics capability.
• VT1XX-CE - Upgrade kit to convert the VT100 or VT125 to word processing version.
• VT1XX-SA - VT100 series tilt/swivel base.
• VT1XX-ST - Terminal stand with casters.

VT180

In 1982 DEC introduced a Z80-based option board which turned the VT100 into a CP/M microcomputer. The option board included 64KB of RAM, a floppy disk controller and an extra serial port, in addition to the Z80. It was also possible to buy a terminal with the option board pre-installed, this configuration was sold as the VT180.

References

[1] Discussion on the classic computers mailing list (classiccmp.org)

Simulators

There are some VT100 terminal simulators that model the hardware and run the original firmware:

• MAME
• PCx80
• terminal-simulator
• VT100 Hax for Retrocomp 2014

External links

• vt100 - documentation at Bitsavers
  • VT100 Series Video Terminal Technical Manual - explains the VT100 hardware
  • VT100-0 Field Maintenance Print Set - schematics
• VT100 User Guide
• VT102 User Guide
  • [Appendix E - VT102/VT100 Differences]
• The Annotated VT100 Firmware
• Raster CRT Typography (According to DEC)
• Simulation of the VT52 and VT100 hardware
• VT100 Oddities