Video and VGA - resistor selections for use with less pins (RamBlade)

Cluso99

I am currently just finalising a pcb design (RamBlade for ZiCog/CPM/PropDos)

I require options for minimum pin counts and resistors.

I will use the 1 pin version of TV, with options for 2 & 3 pin versions as well.

Also, I want to be able to do minimal pin count versions of VGA as an alternative.

For reference, here is thread about minimal pins http://forums.parallax.com/showthread.php?p=796900

I am trying to re-use smt resistors with tiny links for different options.

The keyboard 10K pullups and the 10K/5K for the VGA single pin HS and VS per Phil (PhiPi) will all be done in a single smt resistor package of 8 x 10K 16 pin package (2 parallel 10K -> 5K) and the inverter & buffer (2 inverters) or 2 x exclusive or will be done with an 8 pin 74LVCxxx SOT style chip.

Now, for the series resistors for the VGA option, it seems that 240R for HS, VS and each of the RGB is required. I will need to buffer the RGB since it will likely be driven by 1 common prop pin and 3x30mA will stress the prop. Are the 240R the best for this???

Now for the TV option, 3 pins use 1k1, 560R & 270R. The single pin version was suggested to use 124R (so 120R) series with 191R (so 180R) to ground in parallel with 470pF, although likewise it was suggested that the 191R // 470pF could most likely be dispensed with.

Presuming the 240R are best for the VGA I will have 3 x 240R remaining.... So can I...
* Use 1 x 240R for the single pin TV (or 2 x 240R in parallel -> 120R) ? Which is best.
* Use 1 x 240R and 1 x 480R (2 series 240R) for the 2 pin version of TV ?
* Use 1 x 240R, 1 x 480R (2 series 240R) and add a single 1K1 resistor for the 3 pin TV.

Unfortunately, I want to get my pcb and parts orders away and will not have hardware to test this for another week+

Any help will·be greatly apppreciated Analogue and TV/VGA is not my·speciality

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Links to other interesting threads:

· Home of the MultiBladeProps: TriBlade,·RamBlade, RetroBlade,·TwinBlade,·SixBlade, website
· Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator)
· Prop Tools under Development or Completed (Index)
· Emulators: Micros eg Altair, and Terminals eg VT100 (Index) ZiCog (Z80) , MoCog (6809)
· Search the Propeller forums·(uses advanced Google search)
My cruising website is: ·www.bluemagic.biz·· MultiBladeProp is: www.bluemagic.biz/cluso.htm

Ale

I was having a look at the Spartan 3A board by Xilinx and noticed that they use 4 resistors with values 4k, 2k, 1k and 510R for a 4 bit per color scheme. And that is with 3.3V. Maybe 240R is not the best value...

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Visit some of my articles at Propeller Wiki:
MATH on the propeller propeller.wikispaces.com/MATH
pPropQL: propeller.wikispaces.com/pPropQL
pPropQL020: propeller.wikispaces.com/pPropQL020
OMU for the pPropQL/020 propeller.wikispaces.com/OMU

Cluso99

Ale - is that for VGA or TV (composite video)?

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Links to other interesting threads:

· Home of the MultiBladeProps: TriBlade,·RamBlade, RetroBlade,·TwinBlade,·SixBlade, website
· Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator)
· Prop Tools under Development or Completed (Index)
· Emulators: Micros eg Altair, and Terminals eg VT100 (Index) ZiCog (Z80) , MoCog (6809)
· Search the Propeller forums·(uses advanced Google search)
My cruising website is: ·www.bluemagic.biz·· MultiBladeProp is: www.bluemagic.biz/cluso.htm

Peter Jakacki

Ray,

One of my new designs justs uses just the one value of those little quad smd resnets for both the VGA and TV.

If I use four 470R resnets I get enough to run the standard VGA or the TV signals from 8 I/O. Normally the TV signals would have multiples and sub-multiples of 560R but 470R is a good compromise. I will get to try it out this week.


P.S. Scrub that, I just realized you need something different

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
*Peter*

Post Edited (Peter Jakacki) : 10/5/2009 8:53:26 AM GMT

Cluso99

Peter, your P22 & P23 will give you your 235R & 470R for composite. If you make the P21 pair of 470R parallel resistors a link on the P21 side, then a link to parallel them will be for the G and alternately making the link from the second 470R (making them in series) to the R pin will make the R pin the composite TV pin.

Your current circuit is providing a resistive link between P16, P17 & P18 from the TV thereby causing interference between HS, VS and B :-( see post below.

Please let me know how it goes.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Links to other interesting threads:

· Home of the MultiBladeProps: TriBlade,·RamBlade, RetroBlade,·TwinBlade,·SixBlade, website
· Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator)
· Prop Tools under Development or Completed (Index)
· Emulators: Micros eg Altair, and Terminals eg VT100 (Index) ZiCog (Z80) , MoCog (6809)
· Search the Propeller forums·(uses advanced Google search)
My cruising website is: ·www.bluemagic.biz·· MultiBladeProp is: www.bluemagic.biz/cluso.htm

Post Edited (Cluso99) : 10/6/2009 12:22:39 AM GMT

Dr_Acula

Re Ale: 'Spartan' 'Xilinx' Going off on a tangent, Cluso and I were brainstorming this yesterday. Put a Z80 computer on a xilinx chip. Put a cog on a xilinx chip. Put a propeller on a xilinx chip and use it emulate a z80 computer. Crazy ideas. But then again, pretty much all the chips of the N8VEM seem to be on opencores. With vga drivers et al. This is way outside my area of expertise, but it raises some interesting possibilities. Especially when a propeller can almost do what you want, but not quite due to lack of pins. I wonder what you could do with a propeller and a single FGPA chip?

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
www.smarthome.viviti.com/build

Peter Jakacki

Cluso99 said...

Your current circuit is providing a resistive link between P16, P17 & P18 from the TV thereby causing interference between HS, VS and B :-(
Please let me know how it goes.

As the port pins are always outputs there is no way that a weak circuit can overdrive these pins. They operate as a binary ladder in R/2, R, R*2 values but any "feedback" is purely resistive in the order of hundreds of ohms or more back to a low-impedance I/O pin. The effect that any resistively coupled signals would have on the signal would be negligible. I have run a similar circuit before but this is the first time I have used identical resnets. Anyway I was squeezed on these particular proto boards and that pcb area is either fitted with fiber optic components or an RJ-45 for the AV along with the resnets.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
*Peter*

Cluso99

@Peter, as discussed ofline - my mistake as simplifying the circuit shows they are on the prop side which of course has no effect. May help my design too.

@PhiPi, I was thinking while discussing the circuit with Peter, RGB cannot require 30mA per pin if we are using 240R in series, so buffering the RGB will not be required if driving all from 1 prop pin. However, we will require some drive level for the single pin HS and VS since it is a ladder divider using 10K/5K/5K/10K.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Links to other interesting threads:

· Home of the MultiBladeProps: TriBlade,·RamBlade, RetroBlade,·TwinBlade,·SixBlade, website
· Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator)
· Prop Tools under Development or Completed (Index)
· Emulators: Micros eg Altair, and Terminals eg VT100 (Index) ZiCog (Z80) , MoCog (6809)
· Search the Propeller forums·(uses advanced Google search)
My cruising website is: ·www.bluemagic.biz·· MultiBladeProp is: www.bluemagic.biz/cluso.htm