vLA81 – A ZX81 ULA replacement

vLA81_Tindie
vLA81

The vLA81 is a modern plugin replacement for the ZX81 ULA. It is one of several ULA replacements I have made for members of the Sinclair computer family including the vLA82 for the Spectrum 48K, the vLA128 for the Spectrum 128K (Toastrack) and +2 (Grey case) and the vLA1 for the Sinclair ZX Interface 1.

As they simply don’t make ZX81 ULAs anymore, then unfortunately if the ULA has failed (and there’s not much else on a ZX81 to fail), then options for repair are rapidly diminishing. The vLA81 provides a simple way to keep these icons of 80’s computing going.

Apart from providing the functionality of both the earlier 2C158E/184 ULA (without back porch) and the 2C210E (with back porch), the vLA81 also has a few extras added.

vLA81 features:

  • Fits within the same 40 pin DIL socket outline as the original ULA.
  • Narrow IC pins for easy plugin ULA replacement. In most cases the existing socket will be OK (unless, of course, the existing ULA is soldered in).
  • Provides the same functionality as the 2C210E Sinclair ULA.
  • Video level selectable between standard video (suitable for direct connection to a 75 ohm monitor input) and high sync level (suitable for the modulator input or some video mod boards).
  • Back porch on/off select.
  • Internal 32K memory support (High or Low for the different hires schemes).
  • Programmable user configuration gives access to:
    • Inverse or normal video and choice of black or white border.
    • 50/60 Hz video standard.
    • Ability to map ram to the ROM space (write protect enable/disable – 32K internal ram required).
    • Configuration port socket provided on PCB base for external config switch (optional extra).
  • Tested with an extensive suite of ZX81 software.
  • Ideal for preserving the original ZX81 ULA.
  • Low power consumption.

Download the user manual and install guide here. A guide showing the external configuration switch option can be found here.

Whether you want to just get a faulty ZX81 back up and running, or want to extend the ZX81 with expanded memory and HIRES, the vLA81 can provide what you need.

vLA81_installed
vLA81 in ZX81 issue 1
IMG_0726
vLA81 detail
vLA81_sw1
External config switch (option)
vLA81_switch
External config switch (option)