VGA or not VGA .. that is the question !
Posted: 18 Jan 2015 14:36
Recently i've seen and read quite a lot of stuff about people using PAL/NTSC to VGA converters with homebrew micros and stuff. The reason for this I'm not quite sure, but it seems if though they want their homebrew system to be like a 'Modern' PC.. Personally I think that all homebrew systems should use a TV output as that's part of the charm and gives a true 'Retro' fell. Also practically no homebrew machine uses a screen resolution which warrants a Monitor output. I have an old (15yrs old) JVC CRT TV and the picture quality is excellent and can rival most monitors ! My JVC TV could easily handle 512 x 256 or even 640 x 256 quite easily (perhaps even 800 x 512) , and lets face it everyone has a TV in the house or can buy one very cheaply.
You only need look at the GR8BIT to see the paradox of using a PAL/NTSC to VGA convert an old Retro system (MSX ) so it can use a modern monitor ! The GR8BIT uses a V9938 then a VGA convert board to give VGA output But Why would you want a MSX, using a V938 machine to emulate a PC ??
So you still want VGA output ... OK perhaps you're right... Then why not just use a V9990 it's a great ( inexpensive) MSX compatible video chip... giving VGA output and some powerful screen modes... Max screen resolution being 1024 x 424 (undocumented mode). I could never understand why the GR8BIT didn't use it...bizarre !
The only drawback with the V9990 is it's surface mount and you'll have to design your own Video card . Though you have got a template to look at GFX900 MSX video card and the Technbytes V9990.
The V9990 supports the following resolutions:
mode resolution remark
P1 256×212(424) dualplane patternmode (2 independent planes)
P2 512×212(424) patternmode
B0 192×240(480) undocumented overscan mode (no borders)
B1 256×212(424)
B2 384×240(480) overscan (no borders)
B3 512×212(424)
B4 768×240(480) overscan (no borders)
B5 640×400
B6 640×480 needs a 25.2MHz oscillator
B7 1024×212(424) undocumented mode
Other features of the V9990:
512kB VRAM (4 times as much as on the standard MSX2, so 4 times as much pages!)
A lot faster than V9938/58
Dualplane mode P1: two planes that can scroll independently, with 4 palettes of 16 colours out of 32768 per plane
125 sprites in P-modes, with upto 16 sprites per horizontal line. Any 16×16 block can be used as sprites, with the use of all colours out of one of the four palettes of 16 colours out of 32768
More interrupt-types
Easier programming
Posibility to use larger image size than display size
Interlacing is done by just doubling the picture-size, not by splitting odd-lines and even-lines to different pages, but just the uppper and lower half of the screen
Good priority-support for sprites
You only need look at the GR8BIT to see the paradox of using a PAL/NTSC to VGA convert an old Retro system (MSX ) so it can use a modern monitor ! The GR8BIT uses a V9938 then a VGA convert board to give VGA output But Why would you want a MSX, using a V938 machine to emulate a PC ??
So you still want VGA output ... OK perhaps you're right... Then why not just use a V9990 it's a great ( inexpensive) MSX compatible video chip... giving VGA output and some powerful screen modes... Max screen resolution being 1024 x 424 (undocumented mode). I could never understand why the GR8BIT didn't use it...bizarre !
The only drawback with the V9990 is it's surface mount and you'll have to design your own Video card . Though you have got a template to look at GFX900 MSX video card and the Technbytes V9990.
The V9990 supports the following resolutions:
mode resolution remark
P1 256×212(424) dualplane patternmode (2 independent planes)
P2 512×212(424) patternmode
B0 192×240(480) undocumented overscan mode (no borders)
B1 256×212(424)
B2 384×240(480) overscan (no borders)
B3 512×212(424)
B4 768×240(480) overscan (no borders)
B5 640×400
B6 640×480 needs a 25.2MHz oscillator
B7 1024×212(424) undocumented mode
Other features of the V9990:
512kB VRAM (4 times as much as on the standard MSX2, so 4 times as much pages!)
A lot faster than V9938/58
Dualplane mode P1: two planes that can scroll independently, with 4 palettes of 16 colours out of 32768 per plane
125 sprites in P-modes, with upto 16 sprites per horizontal line. Any 16×16 block can be used as sprites, with the use of all colours out of one of the four palettes of 16 colours out of 32768
More interrupt-types
Easier programming
Posibility to use larger image size than display size
Interlacing is done by just doubling the picture-size, not by splitting odd-lines and even-lines to different pages, but just the uppper and lower half of the screen
Good priority-support for sprites