Does the circuit put out the RGB signal all the time for each component or is it just 1/4 of the time while the remaining 3/4 has no signal at all?

PS: Altera EPM240 is typical equivalent to 190 Macrocells and the 570 is typical equivalent to 440 Macrocells. I thought I would mention them because it is hard to find 'in production' CPLD that will work with 5V0. 

The sync resistors aren't critical. I have a Papilio one that uses series 82.5 Ohm resistors. The Papilio is a Xilinx 3E and I think it is 3v3 IO. The spec says TTL from a 75 Ohm source so you could use 75 Ohm resistors. Anything from 50 Ohm to 100 Ohm won't give problems. 

I have a lead here that I use with a XC9572XL and I think I just used 100 Ohm resistors in that. Correction, just pealed the heat shrink off it and it's a 56 Ohm. I have been using that with Xilinx XC9572XL, Altera EPM240 and EMP570 (3V3 IO) and I haven't had problems. Just make sure you have the sync polarity right for the standard you are using. 

I am assuming you will be driving the sync from the 3V3 IO of the CPLD. If you want to drive from a TTL (5V0) chip then I would go higher than 75 Ohms, perhaps 82 Ohms or 100 Ohms. 

If you end up needing more gates then I suggest the Atera EPM240/570 but there a min 100 pin (QFP100 0.5mm) unlike the XC9572XL / XC9536CL that you can get in QFP44 or PLCC44/84. The Atera chips is much the same - 3V3 IO that is 5V0 tolerant. Altera programmers are cheap to. 

Can I ask ... where did you get the VHDL for the standard 74xx series chips? Is there a library somewhere? It would be handy for me sometimes as I am a VHDL newbee and seeing the old chips would help. In some VHDL I did recently, I couldn't get an asynchronous register load to work. It would be good to see how it was done in the basic 74xx series. Thanks.

Hey there, thanks for the well though clarification. I am not going to use CPLDs actually, I'd rather use discrete 74xx logic chips. What you see in the black background schematic is actually took from EAGLE CAD. As stated in the project description, I'd avoid CPLDs to let (me and) other people to just print a board, buy the chips (in a convenient TSSOP package) and the passives, solder everything and that's it. This avoids the need for a JTAG programmer and should make the soldering job somewhat easy. Anyway, the discrete chips indeed have 3V3 outputs and I'd drive the SYNC lines from the registers outputs. Also note that I will use SCART RGB cable but I still have to understand if I have to put 75 Ohms resistors to ground for video and sync signals (like a PAL SNES cable) or 220 uF capacitors in series (like a PAL GCN cable), as shown in the diagrams at the following link: http://members.optusnet.com.au/eviltim/gamescart/gamescart.htm

For RGB signals the spec is 0.7 Volts into 75 Ohms for both monitors and TV's. It looks like your RGB outputs are currently close to TTL Voh which is much higher so you will need series resistors between each of your R, G and B outputs and the monitor connector. 

Sync is not so easy, it depends on what you're connecting to. For monitors the spec is here - http://web.archive.org/web/20030704041337/www.vesa.org/public/PnD/pnd.pdf

Section 4.5.3.4 - Termination of Synchronisation Signal Lines; Loading
In the case of systems using the TTL logic levels as defined above, the standard termination presented on the synchronisation lines by the display device shall be a nominal 2 K Ohm to +5 VDC.

PAL and NTSC don't have a spec for sync because it is not separate. SCART specifies 0.3 Volts normal and 0 Volts during Sync.

I wouldn't bother with capacitors as the will reduce the video bandwidth and quality. They're are more for 'TV standard' resolutions. 

For ball park figures - 

Your R/2R DAC is lots of 520 Ohm resistors in parallel so I will be lazy and call the output impedance 0 so I don't have to do the math. On RGB you want 0.7 into 75 Ohms from Voh of 3V3 chips. LVTTL spec is here - http://www.designers-guide.org/Forum/Attachments/JDEC_3_3V.pdf

LVTTL Voh is 2.4 Volts. So your series resistor has drop 1.7 Volts so it should be about 182 Ohms. 

A little less 'ball park' - The R, G, B, voltage for 111111 will be Voh * 127 / 128 which means that 'all the other resistors' add up to the ground resistor (560 Ohms) divided by 127 ie 4.41 ohms so take that from 182 Ohms and you're left with about 178 ohms. 

Now reality lol. A Voh of 2.4 Volts is a minimum (worst case) measurement and a typical value would be more towards 3.3 Volts so your series resistor should actually be higher in value. I would *guess*, 220 to 270 Ohms Ohms as no 'typical' value of Voh is specified. If the voltage going into a monitor is slightly high then the monitor will correct it (a little). 

Sync series resistors only need to me *about* 82 Ohms, like I mentioned anything from 50 to 100 Ohms would be fine. You don't need shunt resistors (to ground) for any of the signals. 

In reality, the input impedance to a monitor is 100 Ohms more often then it is 75 Ohms You can measure it with a meter then the monitor is unplugged from power.