ECS Agnus + OCS Denise

[darkcoder]

Hello

 the OCS displays either PAL or NTSC, while an ECS can display both.

What happens with those A500 and A2000 which have the ECS Agnus but OCS denise? My guess is that they can display both modes since it should be Agnus who controls video beam timing, and indeed that's what happens with WinUAE. But I would like to have this confirmed by someone who has a real Amiga with ECS Agnus and OCS Denise.

[sprocket]

I don't have a 2000 handy that has the variations you're talking about but my guess would be that it wouldn't be able to display both since Denise is the main video processor and Agnus controls chipset operation and ram access.

My assumption would be that Denise has to have NTSC/PAL capability for a system to be able to display it but it's only my assumption.

I wouldn't assume because WinUAE demonstrates an effect that it would be the case in real hardware.  The screens are subject to so much software on a UAE system it wouldn't be clear to me that this was because of chipset code.

just my two cents.

[SamuraiCrow]

I used to have an A500 system like that and it works for what you want to do with it.  The problem with not having a Super Denise is that it can't address more than 512k of Chip RAM.  That is a major limitation but since you already have WinUAE, you can probably get by.

[Matt_H]

Many, many 500s and 2000s were shipped like that from the factory. You'll have 1MB chip RAM, PAL/NTSC switchability, but no ECS screenmodes like Multiscan, Euro36, etc., which are added by ECS Denise.

[Zac67]

Matt_H is right - since there are no distinct PAL/NTSC versions of neither OCS nor ECS Denise, either will work in both modes. Vertical scan timing comes from Agnus alone.

An OCS Denise is
- unable to vary the horizontal scan rate, thus no productivity or 31 kHz modes
- unable to produce SuperHires pixel rate (35 ns?)

Actually Denise is not the video chip in the general sense, it's more like the RAMDAC used in Wintel PCs (without the DAC part, this is the external Vidiot). Denise combines the bitplane data coming from Agnus, does the palette lookup (or HAM conversion) and serializes the data for output.

@SamuraiCrow
Denise has nothing to do with the amount of chip RAM available. An OCS Denise will even work fine in an A3000 or A500+ with 2 MB chip mem.

[Piru]

I had such A500 and it indeed could display both modes just fine.

[Crumb]

I had an A500+ motherboard with OCS denise and 1.5MB of chip ram and it worked fine. Of course, it didn't show ECS screenmodes like SuperHires or Productivity but that was not a problem as these modes are quite slow on ECS.

[rkauer]

Crumb wrote:
I had an A500+ motherboard with OCS denise and 1.5MB of chip ram and it worked fine. Of course, it didn't show ECS screenmodes like SuperHires or Productivity but that was not a problem as these modes are quite slow on ECS.

 Capable, but not showed!

[AMC258]

I had an A2000 with an OCS Denise and an ECS Fatter (?) Agnus.  2M Chip RAM, a physical switch for PAL/NTSC, and no ESC video modes.  It would identify as OCS.

[darkcoder]

tnx everyone for the reply, I needed exactly those info!!

 :-D

[voxel]

Another problem will be with the overscan whith genlocks.