NuLA Adapter - IanSB/RGBtoHDMI GitHub Wiki

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 images/nula/adapter1.jpg

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 images/nula/adapter2.jpg

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 images/nula/adapter3.jpg

Solder wire jumpers from each resistor end to J1 - J12 images/nula/adapter4.jpg

Solder a wire jumper from JP1 on the NuLA to J13 on the adapter images/nula/adapter5.jpg

Solder the wires to the ULA header pins 16 and 28 images/nula/adapter6.jpg

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)

The new 6Mhz from the adapter has to be connected to the SAA5050 replacing the original 6Mhz and there are several ways to do this:

Option A: The most direct way is to isolate Pin 19 (TR6) of the SAA5050 by either by bending it out if socketed or cutting and bending it out if soldered and then plug one end of the dupont cable into the 6Mhz out of the adapter and solder the other end to the bent out Pin 19 of the SAA5050.

Option B: Cut the pin of the chip connected to Pin 19 (TR6) of the SAA5050 and then plug one end of the dupont cable into the 6Mhz out of the adapter and solder the other end to Pin 19 of the SAA5050.

Cut IC37 (74LS04) pin 8 for the BBC to isolate Pin 19 on the SAA5050
Cut IC25 (74LS86) pin 11 for the Master to isolate Pin 19 on the SAA5050

Option C: Cut the PCB track between Pin 19 of the SAA5050 and the pin of the chip listed in option B then connect the wire as option B

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

If you have problems getting a clean calibration then try adjusting the 6Mhz delay jumper or try moving the 6Mhz cable to the Inverted 6Mhz pin (Inv6M)

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. (To remove after fully soldering you would need to heat and remove each pin individually and then use hot air to separate the two boards as they are so close together the pads will be connected with solder blobs)