Help to identify this A500 mood.

[arttu80]

It's cool mod, but I guess yo'll stuck with only 512k Chip RAM until swap out 8371 Agnus for 8372 version. But this will maybe require altering JP2 and JP7A jumper settings after the Agnus swap. I would do the swap, but not sure how it will affect these other mods.

[arttu80]

This is not a chip ram mod, this is an additional 512KB as OTHER memory, I suspect that this wires go to a switch.

Ah, Zetr0 was faster than me. Good quality response, Zetr0! Still not sure how you can get 1 Mb chipRAM from 8371 Agnus...

[arttu80]

@arttu80

Actually the 8371 Agnus can address 1MB of CHIP RAM, if you note the image I posted it explains how this is done on a Rev6a A500.
.

Hmm... Very interesting. Not meaning to steal this thread with this topic, but I always was in belief that 8371 Agnus is 512k OCS chip. Actually even SysInfo will support this statement. Ofcourse I believe your words, seems you know little more about HW than I, but still little confused. I actually always replace 8371 with newer when possible (A2k and 500s). Is it possible, that PAL machines are different to NTSC in Agnus chips? I deal with PAL stuff only...

[arttu80]

I gots to reading..... .....  a lot =)


an OCS chip set is just that, it comprises of DENISE, and 8370 Agnus.

an ECS chip set seen on the A500 is a Super Denise and an 8375 Agnus, this is also an A600 as well.

Now this will bake your noodle a bit, what makes the chip set OCS or ECS is in fact the Denise.  If you have a Super Denise installed you essentially have an Enhanced Chipset, as you gain extra screen modes.

Agnus is just an (Address Generator Unit) - depending on what you have 8370, 8371, 72, 74 will determine the address it can generate, it also handles some aspects of video in regards to PAL / NTSC.

the 8370 can address 512KB of CHIP
the 8371 can address 1MB of CHIP
the 8372 can address 2MB of CHIP*
the 8375 can address 2MB of CHIP*

*I should mention that there are some revisions of 8372 and 8375 that can only address 1MB of CHIP - most notably a particular revision in the early rev5.3 A2000's

Sadly I don't think Commodore had any idea when it came to name convention and there are some crazy revisions within each iteration - its quite difficult to get a right answer as well as very easy to be complete confused.

Alexh, I believe a member here, he probably knows more about Agnii than anyone outside the designers at commodore to be honest

I bow you for your replies regarding this topic. You really go for all the trouble explaining details for us whom aren't as enlightened. Great reading, thanks!