Designed for RC2014


I first tweeted about the VT132 in March 2019 I had put together a first prototype in time for mVCF - Melbourne (AUS)


Back then it was simply the hardware implementation of the brilliant work done by Fabrizio Di Vittorio in creating the FabGL library for the ESP32. An ANSI/VT compatible, serially connected terminal with VGA output and a PS/2 keyboard.

But I wanted to extend his work and make a very authentic implementation of the DEC VT100 down to every reasonable detail.

Clearly from the prototype I'd already chosen the form-factor to be a "Designed for RC2014" expansion card for the RC2014 bus.

I then took a break from the VT132 while I worked to finish another little project - the IMSAI 8080 replica

In January 2020 I again tweeted about the VT132 because I'd started to play around with it once more.

I'd added most of the authentic VT100 features I could think of, and decided that since the ESP32 has lots of UARTS and WiFi, that I would include a Telnet over WiFi, AT (Hayes) style modem on a second UART. I'd already developed the modem code for the IMSAI8080 replica, so it was easy to integrate it into the VT132.

This is where the fun/trouble began...

  • FabGL is an Arduino library. Running FabGL @ 800x600 native resolution (800x300 scanline doubled) consumes a lot of the ESP32s internal memory.
  • Turning on WiFi in the Arduino environment on an ESP32 also consumes a lot of the ESP32s internal memory.
  • Moving to the ESP32-WROVER with 8Mb of SPRAM helps a little, but it's still the internal memory that is the limiting resource.
  • The Arduino IDE for ESP32 doesn't let you control and fine-tune all the memory and network resource allocation like the ESP-IDF does.
  • But Espressif thought of that...
    • It is possible to run the Arduino library as a component in the ESP-IDF environment.
    • I was easily able to make FabGL behave as an ESP-IDF component too.

By April 2020 I was able to start posting videos to YouTube showcasing the features of the VT132.


More to come...


VT100 Terminal

The VT100 Terminal:

  • connects to the RC2014 over the Tx/Rx lines (Pins 35 & 36) of the RC2014 Bus
  • takes power from the bus from Gnd/5V (Pins 17 & 18)
  • fully DEC VT100 Escape Code compatible
    • extended escape code support from other DEC VTxxx models
    • extended ANSI escape code support
    • to be detailed on another page (tba)
  • 800x600 native resolution over VGA (DB15 connector) - actually 800x300 with scanline doubling
    • 800x240 viewport in 24 line (native) mode
    • 800x250 viewport in 25 line (enhanced) mode
  • 10x10 character cells in 80 column mode
    • original DEC VT100 font (ASCII 7-bit) with pixel stretching as per the original VT100 hardware
    • original DEC Special Graphics overlay font (inc. line drawing characters)
    • original DEC VT220 Multinational Character Set (MCS) font (8-bit)
    • DEC National Replacement Character Set (NRCS) support (7-bit) (from VT220)
      • implemented for US/UK/Germany/Italy, other countries to follow
    • PC/VGA Code Page 437 font for ANSI compatibility
      • supports DEC Special Graphics mapping to CP437
      • supports NRCS mapping to CP437
  • 6x10 character cells in 132 column mode
    • modified DEC VT100 font (ASCII 7-bit)
    • modified DEC Special Graphics overlay font (inc. line drawing characters)
    • modified DEC VT220 Multinational Character Set (MCS) font (8-bit)
    • DEC National Replacement Character Set (NRCS) support (from VT220) see above.
    • no CP437 support in 132 column mode
  • accurate Smooth Scrolling (requires XON/XOFF as per the original VT100 to avoid dropped characters)
  • interlace/non-interlace mode (simulated: doubled scanlines are either hidden or drawn)
  • PS/2 Keyboard (Mini-DIN 6, PS/2 connector)
    • supports keyboard layouts for US/UK/Germany/Italy, other countries to follow
  • implements all VT100 Advanced Video Option (AVO) features
    • 132x24 (native), 132x25 (enhanced) character resolution
    • additional character attributes - Bold, Blink, Underline, Reverse (and combinations)
    • additional character ROM (NRCS and MCS fonts)
  • implements user programmable answer back as per VT100
  • implements a physical buzzer on the PCB for
    • keyclick
    • bell (^G)
    • margin bell
    • NVRAM error notification
    • non-blocking (operates on a timer interrupt and does not block serial communications)
  • implements 16 colour support
    • complies with ANSI escape code selection
    • use selectable default text and background colours via additional Set-up C screen
  • full VT100 style Set-up screen implementation
    • Activated by Alt-SysReq key-press (usually Alt-PrintScreen)
    • Set-up A (native as per VT100 with minor modifications)
      • added 'T' command to restore default Tab-Stops (from VT102)
    • Set-up B (native as per VT100 with minor modifications)
      • added 'C' command to clear NVRAM
      • 50/60Hz bit replaced by Backarrow Key Mode selection bit (DECBKM)
      • baud rates supported - 300, 1200, 2400, 4800, 9600, 19200, 38400, 57600, 115200
      • fixed serial format 8N1, no current support for 7 bits, parity or 2 stop bits
    • Set-up C (enhanced) enables:
      • DEC/VT font or CP437 font selection
      • 24 line (native) / 25 line (enhanced) mode selection for ANSI compatibility
      • default foreground text colour selection, 1 of 16 colours
      • default background colour selection, 1 of 16 colours
      • ANSI or VGA 16 colour palette selection
    • Set-up D (enhanced) enables:
      • 7-bit ASCII (native) / 8-bit MCS selection (enhanced)
      • 7-bit NRCS country selection
      • keyboard country/language selection
      • personality selection
        • personality (escape code and keyboard code translation) support for:
          • ANSI/VT100, ADM-3A, ADM-31, Hazeltine 1500, Osborne 1, Kaypro, VT52
          • details to follow on a separate page (tba)
    • all Set-up screens include optional help by pressing 'F1' key (enhanced)
  • Non-volatile Storage (NVRAM) support for all terminal settings
    • save settings function - 'S' in Set-up screens
    • restore settings function - 'R' in Set-up screens
    • settings are restored on reset and power-up

Full details of configuring the terminal via the Set-up screens will be covered on a separate page (tba).

Telnet/WiFi AT (Hayes) Modem

The Telnet/WiFi AT (Hayes) Modem:

  • connects to the RC2014 over the Tx2/Rx2 lines (Pins 35 & 36) of the RC2014 Enhanced Bus
  • takes power from the bus from Gnd/5V (Pins 17 & 18)
  • includes a dedicated 6-pin FTDI header with dedicated UART for (re)programming and for debug log monitoring
  • implements a minimal set of 'AT' commands enabling it to behave as a serially connected modem
  • supports storing all 'S' register settings in non-volatile storage (NVRAM)
  • settings can be restored from NVRAM or restored to 'factory' defaults
  • settings are restored from NVRAM on reset and power-up
  • support 'DIAL' mode for outbound connections to hosts
  • supports 'ANSWER' mode for inbound connections including simulated 'RING' cycle
  • does not aim to reproduce every feature and command of any specific Hayes modem
  • connects to a WiFi access point over 2.4 GHz (802.11 b/g/n) as a WiFi station (STA mode)
  • cannot currently act as a WiFi access point (AP mode) - but this would be possible if it is a feature that people want
  • supports Telnet and TCP socket protocols for connecting to hosts
  • supports serial baud rates of 4800, 9600, 14400, 19200, 38400, 57600, 1152000 from the UART
    • making it compatible with all the speeds of the RC2014 Dual Serial Module SIO/2 or similar
    • does not currently support 'autobaud'
      • but is selected by a press button switch on the PCB
      • the chosen speed is stored in NVRAM and persists through resets and power cycling
  • supports CTS/RTS hardware flow-control over a 6-pin modified FTDI style modem header (not the RC2014 Enhanced Bus)

A full list of the 'AT' command set implemented and details of all the 'S' registers and their use will be covered on a separate page (tba).


The VT132 is currently in a closed Beta and is expected to be ready in July 2020.

Expression of interest

I am accepting expressions of interest via email. If you send email to info@thehighnibble.com I will add you to the list.


Dimensions (built)

Designed for RC2014

Conforms to standard RC2014 card dimensions

Weight (built)

0.1 lbs

0.045 kg


5VDC @ 500 mA (max., < 100mA typical) - Powered from RC2014 Bus or via FTDI or Modem connectors (jumper selectable).

Dimensions (boxed/shipped)

7 1/2" x 5.5" x 2"

190mm x 140mm x 50mm

(width x height x depth)

Weight (boxed/shipped)

less than 0.44 lbs

less than 0.2 kg


Operation Manual

Last Updated: 6/14/2020, 9:33:14 AM