Amiga hardware info, help and support with a focus (but not limited to) North American NTSC experiences. Open to all.
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Seattle, WA, USA

by intric8 posted Wed Jan 31, 2018 6:38 pm

In the world of NTSC and PAL, the Agnus chip plays a prominent role. She is one of the three main chips from the Amiga OCS (Original Chip Set). She controls RAM addressing as well as key components of the visual display - particularly video timing.

There were several versions of Agnus created over the years by Commodore. Based on a previous discussion around here about the Agnus chip, I wanted to see if I had a proper replacement (going from PAL to NTSC). But since I personally didn’t know which chips were which I needed to do a little bit of homework first.

Here’s what was created back in the day for reference:
  • OCS Agnus which can address up to 512 kB of Chip RAM (PLCC versions add 512 kB of pseudo-fast RAM)
    • 8361 (DIP) - Amiga 1000 (NTSC); Amiga 2000 model A (NTSC)
    • 8367 (DIP) - Amiga 1000 (PAL); Amiga 2000 model A (PAL)
    • 8370 (PLCC) - Amiga 500 to Rev 5.x (NTSC); Amiga 2000 model B to Rev 4.5 (NTSC)
    • 8371 (PLCC) - Amiga 500 to Rev 5.x (PAL); Amiga 2000 model B to Rev 4.5 (PAL)
  • ECS Agnus which can address up to 1 MB of Chip RAM
    • 8372 - no data*
    • 8372A - Amiga 500 from Rev 6 (NTSC/PAL); Amiga 2000 model B from Rev 6.0 to Rev 6.3 (NTSC/PAL); Commodore CDTV
    • 8375 (318069-16 only) (PAL) - Amiga 500 from Rev 6 (PAL); Amiga 2000 model B from Rev 6.4 (PAL)
    • 8375 (318069-17 only) (NTSC) - Amiga 500 from Rev 6 (NTSC); Amiga 2000 model B from Rev 6.4 (NTSC)
  • ECS Agnus which can address up to 2 MB of Chip RAM
    • 8372AB - Amiga 3000 from Rev 6.1 to Rev 8.9 (NTSC/PAL)
    • 8372B - Amiga 3000 Rev 9 (NTSC/PAL)
    • 8375 (PAL) - Amiga 500 Plus; Amiga 600 (PAL)
    • 8375 (NTSC) - Amiga 600 (NTSC)

Agnus was replaced by Alice in the Amiga 4000 and Amiga 1200 when the AGA chipset was introduced in 1992.
Well, boo.

Agnus Slang

Poor Agnus got called a lot of names, and most not particularly nice. It seems to depend on which continent you’re from, but I’ve heard various names thrown around for the various levels of Agnus’. I think it goes something like this:
Agnus = 512KB
Fat Agnus, Obese Agnus = 1MB
Super Fat Agnus, Super Obese Agnus = 2MB

And, I think, if you're running "Super Fat Agnus" on Phoenix/500/2000 you have to use what's called the MegaChip, which is a small board that sits into the slot that Agnus used to reside in, and your 2MB Agnus fits into the board. With the A3000 you were good-to-go.

My own personal stock of extra Agnus chips:
2MB MegaChip (with Super Fat Agnus), and 2 8372A 1MB "Fat" Agnus chips.

Here’s what I know:
  1. My daily-driver A2000 is running the ECS 8375 (PAL), which has 2MB of Chip RAM.
  2. I have 3 spare loose chips.
    1. Two: 8372A (318069-02) - this is an ECS 500/2000 1MB chip. I don’t know if mine are PAL or NTSC, but assume they are NTSC.
    2. 8372B (318069-03) - this is a 2MB Agnus. Again, I don’t know if it is NTSC or PAL. The one in my daily is PAL. I have a sneaking suspicion this one is NTSC, as I have the original box and it was marked NTSC. That being said, I’ve never had any issues with it and my 2000 looks, smells and acts like an NTSC machine through and through.

In regards to our previous discussion about maybe making my Phoenix 100% NTSC, I think if I put one of my loose 8372A’s in the Phoenix in theory that should do the trick (if it’s an NTSC chip, which they all should be).

And I think my loose 8372B is in fact an NTSC chip. I wonder if i should put it in my daily driver (which doesn’t really have any issues except the viewable 4:3 is slightly off-center) or leave it be?
An NTSC 2MB Super Fat Agnus? Why yes, I think I do!
What's really interesting about that is that in the Phoenix's user manual, it claims to have full support for this chip built in... The Agnus for the A3000. Really? With no mods? Seems hard to believe.

To more tests! <3
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by Bulletdust posted Wed Jan 31, 2018 11:42 pm

Using a Super Obese Agnus out of an A3000, swapping some dram chips and some jumper modifications, you can actually convert a standard Rev 6a A500 (non plus) to 2MB of chip ram without the need for any additional add on boards: ... otherboard

From what I can tell, that 8372B, P/N: 318069-03 is the exact Agnus you need for 2MB chip ram and PAL.

Of course a far easier way to achieve 2MB of chip ram is just to use an A1200!
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Seattle, WA, USA

by intric8 posted Thu Feb 01, 2018 11:58 am

A little more info.

Reading through the MegAChip manual, there definitely were Super Fat/Obese Agnus chips that were set PAL/NTSC (but could do either) based on the serial numbers. Makes me wonder how many there were...

MegAChip Manual:
The number needed is 8375 (see figure 1). You
also need to check the part number on the chip which designates whether it is for
NTSC or PAL use. Part number 318069-11 is for NTSC use and part number
318069-10 is for PAL operation.
You can see in my photo above that my spare is "318069-03". I don't know what my daily driver's serial number might be.

So those other chips are out there somewhere. They do exist.
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by Bulletdust posted Fri Feb 02, 2018 1:28 am

So those other chips are out there somewhere. They do exist.

Like an X-File..... ;)
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Seattle, WA, USA

by intric8 posted Fri Feb 02, 2018 9:12 am

I actually found one. Just can't decide if I really need it anymore. Doesn't seem like it.
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Seattle, WA, USA

by intric8 posted Mon Feb 12, 2018 8:26 pm

Well... look what I found. This is one of the NTSC Super Fat Agnus chips recommended by MegAChip: Part number 318069-11!
NTSC Super Fat Agnus 318069-11

I don't think I could use this in the Phoenix without mods, but I know I can snap this into my daily driver A2000! I'm not going to do it right this minute, but there's a weird part of me that can't wait to see that show up in SysInfo soon. Will it change anything? Nope!

Maybe the Winter Olympics affecting are me. ;)
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Zippy Zapp

by Zippy Zapp posted Tue Feb 13, 2018 1:35 pm

Nice find. The only 8375 I have for my Mega Chip is dead. Do you still have the MegaChip for that 2000?
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Seattle, WA, USA

by intric8 posted Tue Feb 13, 2018 2:56 pm

I have a 2MB MegAChip in my daily 2000, but its with a PAL/NTSC chip that reports to SysInfo as PAL. And I have a spare MegAChip board as well. This new Agnus is the first 2MB NTSC Super Fat Agnus I've run across.

I have a fun project for my 2000 in the near future which will include this Agnus.

  • PSU upgrade. I have a Big Foot PSU waiting for its new home.
  • I got a NOS Kickstart Switcher from cbmstuff. It's not often, but every now and then I run across something for KS 2.0 that would be nice to run.
  • And since I'll have the PSU/tray out of the way, I'll pop this new Agnus in and see what happens! Shouldn't notice a single thing, honestly, except the SysInfo Report. So dumb, I know, but I'm really curious.
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Zippy Zapp

by Zippy Zapp posted Wed Feb 14, 2018 8:26 am

Cool. Sounds like some good upgrades. Let me know how that kickstart switcher works out. I have been debating on getting one for my 2000 too. It has 2.04 installed now + on old, I am sure failing, quantum SCSI drive that sounds like it is going to croak. I have to hook up the Zip drive and try to backup all those files from the 80's/90's.
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Seattle, WA, USA

by intric8 posted Wed Feb 14, 2018 9:20 am

The one piece I need to research is dual Workbench partitions. I have 1.3 installed and it autoboots of course. But once I install the KS switch and flip to 2.0, how do I tell it to go seek out a different drive with WB 2.04 on it (e.g. DH3:) rather than the current drive set to zero?

It's probably not a big deal nor hard to do, but I've no idea how to do that. Funny - on my Phoenix - which is maybe were I should start the experiment since she's such a Frankenstein little creature already - when I flip over to 2.0 it still autoboots into WB 1.3 but with a funky color palette.

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