SuperHiRes mode on A500 rev 6a

Hi I have A500, rev 6a.
denise 8362R8
agnus 8372A
kickstart 2.04 v37.175 (I also have 2.05 v37.299)
All other chips on the motherboard are the same as here http://amiga.resource.cx/photos/a500,5

As I understand, I can only have low-res and hi-res video modes, with 320 or 640 pixels per line (140ns or 70ns).
Is it possible to upgrage my Amiga to enable the SuperHiRes mode, with 1280 pixels (35ns)? If yes, do I need to upgrade both denise and agnus or just denise is enough?
Also, do I need any special monitor to use SuperHiRes mode? Will modern LCD tv work?

[AmigaHope]

Hi there!

Your current Agnus is already an ECS Agnus, so you don't need to replace it, however you should make sure your system is configured for 1M chip RAM as working in Super HiRes (as well as Hires in general) can be chip memory hungry. You can do this by either soldering extra RAM onto the 6A motherboard (you can see there are spots for it) and adjusting jumpers, or you can adjust the jumpers so that a 512k trapdoor expansion becomes chip RAM.

Next you will need to upgrade to Super Denise, as your old Denise is an OCS chip. You need a 8373 Denise, part number 390433-02 (the Denise in the A600 is the wrong form factor so won't work, but the ones from other ECS Amigas should work).

After that, AmigaOS 2.04 will have native support for Superhires, although upgrading to AmigaOS 3.1 is strongly advised as that will give you much finer control over the screenmodes possible.

Your TV will probably not sample the analog signal fast enough to display SHires in full resolution, as it is far far higher horizontal resolution than produced by any other consumer 15Khz device, so most TV analog to digital converters will not expect such a high pixel density. You'll still get an image, one that's higher resolution than normal Amiga hires, but the pixels probably will sort of blur together. To get discrete pixels at that resolution you basically need a high-end fully-analog CRT (preferably a multiscan that has a screen DPI meant for higher resolution displays).

For instance using SHires on my 1084, the analog circuitry is capable of putting out that resolution, but the physical DPI of the phosphor layer wasn't high enough to perfectly show the pixels. On an NEC multisync I had though, the pixels showed up perfectly since the DPI of the screen was designed to show resolutions like 1280x1024.

If you use an analog->digital upscan converter, it needs to sample at a high enough resolution -- most don't, for the same reason that most TVs don't -- they just assume the input device is putting out pixels that are roughly square at maximum.

Digital->digital scan converters almost universally will not work -- not even the one built in the A3000 handled Superhires properly. The only exception I know of is the Indivision ECS.

Also bear in mind that Superhires is still limited to the OCS/ECS DMA rate, so it can only do 2 bitplanes at 35ns (i.e. 4 colors) and it will eat into CPU bus access cycles. Consequently performance on a 4 color SuperHires screen will be exactly the same as a 16-color Hires screen. Also, the ECS Superhires mode is limited to an overall palette of 64 colors, though I don't know the exact reason why this is.

Still, it's a pretty cool mode to play with. =)

Note that in addition to Superhires mode, you get "Productivity" 640 horizontal pixels at around 31Khz, which is similar enough to the original VGA sync rate that many VGA monitors will work out of the box on it. You can play with the chipset in AmigaOS 3.x to get other refresh rates, with the limitation that you are stuck with the 35ns pixel clock at 2 bitplanes.

Originally Posted by AmigaHope

Next you will need to upgrade to Super Denise, as your old Denise is an OCS chip. You need a 8373 Denise, part number 390433-02 (the Denise in the A600 is the wrong form factor so won't work, but the ones from other ECS Amigas should work).

Is Denise from A600 same chip just different package, or is there any difference inside as well? If it's just a package, can make a smd to dip adapter.

I'm asking because they are not very easy to find, so if it's easier to find the one from A600, I could just use it.

[Jope]

It is electrically the same, so you could do an adapter. Let us know how it went :-)

[dalek]

Adaptor already done (by Mattias?):
https://oshpark.com/shared_projects/3jI9QUST
(from https://www.amigaworld.de/hardware/plcc-dip-adapter/ )

Looks like they are (Super Denise) unobtanium. It may be easier to find entire amiga with Super Denise

[AmigaHope]

Originally Posted by amigo500

Looks like they are (Super Denise) unobtanium. It may be easier to find entire amiga with Super Denise

Maybe find dead A500+ for parts or dead A600 and go the adapter route (carefully bending pins around to fit PLCC adapter).

Dead A3000 would be better off repaired than used for parts, unless it's super severely damaged. (Honestly same for dead A500+ -- rev 8 mobo better than rev6a).