NuLA Adapter

Nula Adapter Installation

Before starting, check that 6Mhz is being output on JP1 of the Nula (near the JTAG header)
If that isn't being generated, contact RobC for a firmware update (see: https://stardot.org.uk/forums/viewtopic.php?p=427323#p427323 ) or consider using the clock fixer to generate an alternative 6Mhz

Push the pin header J14 of the adapter into the JTAG holes on the NuLA

Only solder the GND pin (2nd from edge) as soldering multiple pins will make it very difficult to remove if required
The other pins are only used for JTAG reprogramming

Heat up the GND pin with a soldering iron and adjust the adapter board until it is lying flat on top of the resistors with just their ends visible

Solder wire jumpers from each resistor end to J1 - J12

Solder a wire jumper from JP1 on the NuLA to J13 on the adapter

Solder the wires to the ULA header pins 16 and 28

Pick up the Hsync and Vsync outputs of the 6845 (Pin 39 = Hsync, Pin 40 = Vsync) and connect them to the adapter using dupont cables. You can solder one end to the 6845 pins and plug the other end into the HSYNC and VSYNC inputs on the adapter board. (Do not modify or cut the 6845 pins)

Isolate Pin 19 (TR6) of the SAA5050 by either by bending it out if socketed or cutting and bending it out if soldered. Alternatively you can cut the pcb track connected to that pin or cut the pin of the TTL chip connected to it. (Check BBC or Master schematic for details of which chip)

Connect the 6Mhz out of the adapter to pin Pin 19 of the SAA5050. Plug one end of the dupont cable into the 6Mhz out and solder the other end to pin 19

Alternatively try connecting the Inv6M which is the inverted version of the 6Mhz if you have any problems with the non inverted 6Mhz.

Jumpers
The Sync jumper setting allows 0, 1 or 2 gate delays (default 0 delay)
The "C" setting is Composite bypass which bypasses the sync regenerator and uses the BBC composite sync fed to the hsync input
The 6Mhz delay jumpers allow 0, 1, 2 or 3 gate delays (default 1 delay)

Usage
Connect the NuLA adapter to an RGBtoHDMI with a 12 bit extender fitted using a 16 way ribbon cable.
Select one of the NuLA profiles in the BBC CPLD
The NuLA 3bpp Mode7 profiles don't show the extra NuLA colours in mode7 but use the high quality mode7 deinterlacing.
The NuLA 12bpp Mode7 profiles will show the extra NuLA colours in mode7 but only use weave deinterlacing in mode7.

For each profile, run the auto calibration in mode 7, preferably using the mode7 calibration test pattern and also mode 0, then save the results.
After that you would only need to run the calibration again after a software upgrade.

A mode 7 calibration test program can be downloaded here: https://raw.githubusercontent.com/wiki/hoglet67/RGBtoHDMI/images/Mode7_Calibration.zip

Testing
Use *VNPALETTE to start the palette programming menu and use R and Shift R then G and Shift G then B and Shift B to step up and down the 16 possible levels to confirm they are displayed correctly.

If you are happy that everything is working and reliable after several days testing, you can solder the remaining JTAG pins for extra mechanical strength and that will also allow reprogramming via J15 but it will be very difficult to remove after that.