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Old 16 May 2018, 11:53   #1
Marchie
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A2000, 2mb PAL Agnus in NTSC?

Hi Amigans,

I'm looking at upgrading my NTSC 2000 to 2mb chip either with this hack or simply with a Megachip board, but 2mb NTSC Agnus' are nearly impossible to find whereas PAL ones are more common.

Are there frequency issues with using a PAL Agnus? After all the motherboard is the same in NTSC and PAL versions anyway right? My machine was originally PAL and I've just swapped the jumpers and crystal so I can run a Video Toaster.

If I try the hack - are there any 8375 Agnus' that are pin-compatible with the 8372B?

Thanks in advance to anyone who can help!
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Old 16 May 2018, 15:20   #2
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Heh, I had just the opposite problem.

All the unsold MegaChip's I could find came from USA and all were fitted with the NTSC 8375 2MiB Agnus (318069-11) and I wanted PAL. In the end I pleaded on here and some nice soul sent me a PAL Agnus (318069-10). I think I just put the NTSC one in storage.

I think if you talk to tborro here or on Amibay he can get you an NTSC 8375 2MiB Agnus.

Make sure you get the correct one.
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Old 16 May 2018, 15:34   #3
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As you have probably noticed, there is a bewildering assortment of different Agnus versions. Here is a good list of the different versions, translated from a French website. http://translate.google.fr/translate...hl=fr&ie=UTF-8

Its better to disregard the 8375 number on the chip and refer to the part number on the chip. For example p/n 318069-xx can be found labelled as 8372 or 8375. They are interchangeable. The xx represents whether the chip is PAL, NTSC, switchable PAL/NTSC, and whether its 1 or 2 MB. The only 8375 chips that are not compatible are the ones labelled 390544-xx. These are for the A500+ and A600 and are not pin compatible.

A PAL Agnus will work in an NTSC Amiga. You can even use NTSC screenmodes in Workbench, or switch to NTSC in the early startup menu. The internals of the Agnus supports both, but the pin that allows hardware selection was removed in the 8375 Agnuses. There is a slight difference in clock frequency between PAL/NTSC Amigas, but it won't cause any problems if you use an Agnus that is a different video format to what the Amiga is.

Last edited by A4000Bear; 16 May 2018 at 15:39.
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Old 16 May 2018, 16:32   #4
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Thanks for all the helpful info.

A4000Bear-

Thanks for that list, it's more thorough than the one of the BBOAH. So a PAL 2mb 318069-xx can be swapped with my existing 318069-029 without failing or exploding, but it will ignore the NTSC jumper on the mobo and default to displaying PAL resolutions (unless I set it to NTSC from the boot menu each time)?

The video Toaster is pretty sensitive so I need to make sure it will play nice...

On that subject, will a 2mb Agnus work while there's only 1mb chip installed? (I imagine it would be wise to test the chip before I start soldering and de-soldering RAM chips from my motherboard)


alexh-

Thanks for the info. Maybe now is the time I should start pleading for a kind soul to sell my an NTSC Agnus... If there's anyone out there, please PM me with an offer, I'll be your bestest ever friend, I promise.
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Old 17 May 2018, 11:17   #5
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Quote:
Originally Posted by Marchie View Post
On that subject, will a 2mb Agnus work while there's only 1mb chip installed? (I imagine it would be wise to test the chip before I start soldering and de-soldering RAM chips from my motherboard)
yes!
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Old 17 May 2018, 11:26   #6
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Quote:
Originally Posted by A4000Bear View Post
As you have probably noticed, there is a bewildering assortment of different Agnus versions. Here is a good list of the different versions, translated from a French website.
I'm pretty sure that is the list I wrote on here years ago.


Quote:
Originally Posted by A4000Bear View Post
A PAL Agnus will work in an NTSC Amiga. You can even use NTSC screenmodes in Workbench, or switch to NTSC in the early startup menu.
Not sure that games honour the switch in early startup?
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Old 17 May 2018, 11:44   #7
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So a PAL 2MB 8375 318069-xx can be swapped with my existing 1MB 8372A 318069-029 without failing or exploding
I very much doubt it. Otherwise they would not have made the 1MB 8375 318069-17
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Old 17 May 2018, 16:33   #8
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Quote:
Originally Posted by Marchie View Post
Thanks for all the helpful info.

A4000Bear-

Thanks for that list, it's more thorough than the one of the BBOAH. So a PAL 2mb 318069-xx can be swapped with my existing 318069-029 without failing or exploding, but it will ignore the NTSC jumper on the mobo and default to displaying PAL resolutions (unless I set it to NTSC from the boot menu each time)?

The video Toaster is pretty sensitive so I need to make sure it will play nice...

On that subject, will a 2mb Agnus work while there's only 1mb chip installed? (I imagine it would be wise to test the chip before I start soldering and de-soldering RAM chips from my motherboard)
That is correct. As your A2000 is originally NTSC, you already have the appropriate 28.6 MHz oscillator installed (PAL is 28.3). Your video toaster should work as well as it does now, once you select an NTSC screenmode. You may find it more convenient to select the NTSC screenmode within Prefs on Workbench and save the changes. Your Amiga will then boot automatically into NTSC without any further intervention on your part (but only when you boot from that particular disk). You can even do this change before you install the new Agnus.

The 2MB Agnus will work with only 1 MB of Chip RAM present.
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Old 17 May 2018, 17:43   #9
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All useful info, thank you!

I'm not worried about games - I have other stock machines for that, just interested in productivity software for this machine.

I found this page but it seems to muddy the waters rather than clear them - that claims to describe the various part numbers and it says that the 318069-10 is a re-packaged 390554-01?

Never understood what 'VBB' stood for either...
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Old 18 May 2018, 03:56   #10
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Never understood what 'VBB' stood for either...
VBB described here:

http://www.amigawiki.de/lib/exe/fetc...us_reworks.pdf

Check if you need to do the rework. I believe they were labelled VBB to indicate rework for the Vbb pin may be required.
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Old 18 May 2018, 09:58   #11
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That doesn't tell you what VBB actually is.

It stands for "Voltage Back Bias" also known as the substrate-bias voltage. Tuning the bias adjusts the threshold voltage of the transistors inside.

The 8375R0 must have a VBB generator on the silicon which why it doesn't have a VBB pin. But presumably in some circumstances it didn't work for the application and so instead they made the 8375R2 with VBB bonded out to pin so you could adjust it on the PCB?

Exactly why all of a sudden CSG chips needed an external VBB I don't know. Presumably some sort of temperature issue?
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Old 18 May 2018, 11:02   #12
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Quote:
Originally Posted by dalek View Post
VBB described here:

http://www.amigawiki.de/lib/exe/fetc...us_reworks.pdf

Check if you need to do the rework. I believe they were labelled VBB to indicate rework for the Vbb pin may be required.
Very helpful, thank you!
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