A500+ vs. A600

[psxphill]

Zorro I vs A600 trapdoor expansions

A500+ is better. The a600 trapdoor is essentially ram+rtc only, the same as the trapdoor in the A500. It's only the A1200 trapdoor that is equivalent to the expansion port on the A500+.

However the A500+ does not support Zorro I, those are used by the Ranger add on (and also the third party versions that were actually released) for the A1000 and are just a different shape to Zorro II cards.

Officially the slot on the side of the A500+ is called the "86-Pin Slot Expansion" and it's roughly compatible to the A2000 CPU slot, some accelerators were compatible with both. http://amiga.resource.cx/exp/supra28 The A2000 board is shaped like that because it's the same one used in the A500 version, it's just in a box and has a pass thru. AFAIK you can use the A500 version in an A2000 as well.

Personally a 1.3 A500 and a 3.1 A1200 is the way to go.

[psxphill]

There was a PC emulator card for the A600's trapdoor, but it is very rare. The IndivisionECS can be mounted in here too on top of one of Jen's chip ram expansions (A603, A604).

That board was available for all the a500/a2000 as well.

http://amiga.resource.cx/exp/powerpc

The a600 slot is also hoked up to the chip register bus, which is how the indivision ECS can be placed there. AFAIK there is no equivalent to that on any other Amiga.

There are some signals on the a600 slot from the 86 pin expansion. However if it is possible to use it for an accelerator or scsi host adapter, either nobody knows how to go about it or there isn't enough room for that and the chip ram (and for jens it would make sense to still allow the IndivisionECS in the slot).

On the other hand you can get 86 pin expansion peripherals, so the a500 is more expandable than the a600. Although I wouldn't buy either of them to expand them that much (although I did back in the day). An action replay cartridge for the a500 is a pretty cool retro thing to have, but I'm not really into WHDLoad. I'd rather run off floppies (or at least virtual floppies).

[psxphill]

I don't know if the A500+ would have problems with a 1.3 rom.  My guess (and only a guess) (someone out there knows the answer to this) is that it would not be able to address the second meg of chip ram.  Can A2000s or a500 with a megachip address 2 megs of chip ram with 1.3 roms?

Even Kickstart 1.2 could detect 2mb of chip ram.

http://wandel.ca/homepage/execdis/exec_disassembly.txt

Code: [Select]

       ; Having figured out the end address of expansion memory (in A4),
        ; and the value to use for ExecBase (in A6), we now check how much
        ; chip memory we have.  Any memory in the first 2 megabytes of
        ; address space is considered to be chip memory.  Less than 256K
        ; of chip memory is considered a fatal error.

FC0208  lea       0,A0              Start looking at location 0.
FC020C  lea       200000,A1         Don't look past 2 megabytes.
FC0212  lea       FC021A(PC),A5     Set the return address.
FC0216  bra       FC0592            Go check the memory.
FC021A  cmp.l     #$040000,A3       Do we have at least 256K of chip memory?
FC0220  bcs.s     FC0238            Bomb if not.

However reset resident programs won't work if you have more than 512k because of this validity check (which wasn't fixed in Kickstart 1.3 either).

Code: [Select]

       ; We come here if the cold start capture vector was zero, or
        ; upon return from the cold-start capture code.  We continue
        ; to verify the ExecBase structure.

FC0184  bchg      #1,BFE001         Flip the power light to bright.

FC018C  move.l    FC0010(PC),D0     Check the version/revision numbers
FC0190  cmp.l     $14(A6),D0        stored in ExecBase against those in ROM.
FC0194  bne.s     FC01CE            Go reconfigure memory if no match.

FC0196  move.l    $3E(A6),A3        Get end address of chip memory.
FC019A  cmp.l     #$080000,A3       Greater than 512K?
FC01A0  bhi.s     FC01CE            If so, it must be invalid.
FC01A2  cmp.l     #$040000,A3       Less than 256K?
FC01A8  bcs.s     FC01CE            If so, it must be invalid.

There are a couple of solutions to that problem:
http://eab.abime.net/showthread.php?t=78932

I assume 1mb agnus showed up (or at least the first time someone tested 1mb chip ram with RAD: was) after the Kickstart 1.3 mask roms had been ordered but before the Workbench 1.3 floppy disks and Manuals were. I don't know if the official workround helps with 2mb chip ram. Burning a modified EPROM is the best option, but unless you use RAD: then you might not be that bothered.

The 256k minimum chip ram would make it unusable on an unexpanded http://scacom.bplaced.net/Collection/velvet/velveten.php