Video µLA - Replacement for the BBC Micro ULA

Video µLA (mu-L-A, mu being the greek letter used for micro) is my design of a replacement for the hard to find video ULA used in the BBC Microcomputer System, Model A, Model B and Master 128.

Video µLA can replace the early 5C094, the VC2023, or the VC2069.
The motherboard patch required for the VC2023 will not affect the operation of Video µLA.

The FPGA design is in part based on code from the BeebFPGA project by Mike Stirling.
I have done considerable work to allow Video µLA to work seamlessly in the original machines, along with extensive testing in both Model B and Master 128.

Video µLA can be used as a direct swap substitute for the original ULA, but can also add some extra functionality.

In the BBC graphics modes 0 to 6 any of the colours can be redefined to be any from a palette of 4096 colours using 4 bits for each of red, green and blue. For example in Mode 2 you can define 16 different colours, such as a grey scale.

Control of the palette is done using registers compatible with Rob Coleman's Video NuLA.
Note: presently Video µLA does not implement NuLA's scrolling and attribute modes.
The link to the NuLA manual can be found in this StarDot post: https://www.stardot.org.uk/forums/viewtopic.php?p=176865#p176865

To enable the extended NuLA compatible registers &FE22 and &FE23, the included jumper lead must be connected from the A1 header on the underside of the Video µLA PCB to the BBC Micro's address line A1. In the Model B this can be easily found on pin 37 of the 6522 VIA IC3. See the image in the gallery.

Being almost the same size as a 28-pin DIP IC, Video µLA will also fit in a Master 128, even beneath an internal co-processor carrier.

If you use analogue palette colours then the BBC's output cannot display correctly on a monitor with digital TTL inputs. However the original palette will work correctly. Monitors that expect digital TTL inputs include unmodified Microvitec Cub monitors. A more modern television with an RGB capable SCART should work correctly when used with a SCART cable containing appropriate resistors. I highly recommend Ian Priddy's cables from Retro Computer Shack.

I have included some screenshots in the picture gallery.

If you have any questions please feel free to contact me!