---====UPDATE====---- A3000 Rom help needed

[da9000]

amesie2 wrote:
Thanx everyone for the help I am confident the new roms will get me running again.

All is well that ends well :-)

I'm still interested though in someone chipping in on TJ's question:

TJLazer wrote:
 Yes I had to get these special "ROM Tower" ROMs for the rear sockets to make it work in my 3000.

BTW, anyone know what kind of ROMs these special ROMs are?

[TjLaZer]

The guys at software hut are upright guys, I explained my situation and they offered to take the originals back and send me the right ones. I decided to keep the originals as I have a 3000D on the way which needs 3.1 roms as well that they might work in and if not I can send them back for another set of rear 3.1 roms which has been OK'd by software hut already. The second set of roms cost me only 35.00 plus shipping they gave me a break on the second set since I already oredered one set.

That is funny, that same senario happened to me 7 years ago!  I went back and forth and they were great to deal with. Swapped like 3 sets of ROMs until I finally got it working!  It was a hell of a journey getting 3.1 running in my 3000!  A big thumbs up to Software Hut, sounds like they are used to this issue with the 3000's.

[mikolas]

Older A3000s (like mine) had EPROM pinout designed for 27C2048 EPROMs whereas the ROM pinouts for later production runs are for 27C400 EPROMs. ROM tower is just an adapter to make the pinout of newer ROM chips compatible with the rear sockets. You could also burn your own ROM image from standard ROMs to a pair of 27C2048s and would then have a pair of rear socket ROMs.

Mikko.

mikolas wrote:
Older A3000s (like mine) had EPROM pinout designed for 27C2048 EPROMs whereas the ROM pinouts for later production runs are for 27C400 EPROMs. ROM tower is just an adapter to make the pinout of newer ROM chips compatible with the rear sockets. You could also burn your own ROM image from standard ROMs to a pair of 27C2048s and would then have a pair of rear socket ROMs.

Mikko.

Looking at the A300D shematics, I notice the pinout for U180-181 vs U182-183 are totally different.

I have never seen an A3000 with anything in sockets U182-183 and the ROMs I have for the A3000D in U180-181 worked perfectly fine in an A3000T.

Could somebody give me more explanation here... just so I go to bed a bit less dumb?

[amesie2]

@eslapion

I am also confused  :crazy: over the 182-183 socket thing. I would guess that the pinouts for the roms might be reversed since they would go upside-down in a rom tower.
I was told by Software Hut that if I had a rom tower the roms they sent would work fine.

Does someone have a rom tower in a 3000D that they could look at the pinouts somehow?

[TjLaZer]

Apparently if you had a ROM tower and have those rear sockets those 27C2048 EPROMS will work.  I think those were for developers back in the day or some $hit.

Looking at datasheets here reveals that the pinout for the 27C220 and 27C2048 is perfectly identical. The schematics of the A3000D claims U182-U183 to be compatible with that chip format.

However, the 27C400 used in U181 and U180 are completely different. Also, the 27C400 can either be addressed as a 512kbitx8 chip or 256kbitx16. Since pin 31 is tied to Vcc on U180-U181 then this permanently forces the chips in these sockets to be in word mode (256kbitx16).

If you have two 27C400 chips in U180-U181 then only half of these chips would be used to carry a 512kbytes kickstart such as 2.04 or 3.1. Perhaps using a DPDT switch with such chips would allow for a dual kickstart system.

From what I read, a ROM tower (which I have never seen) allows the use of 27c400 chips in sockets U182-U183 which are normally only to be used with 27C220 or 27C2048.

Also, the pinout for the 23c series of ROMs used in the Amiga 1200 and 4000 appear to be perfectly compatible with the 27C400 except for one less address pin. 27c400s are 4Mbit chips while the 23c series used in the 1200/4000 are 2mbit chips.

That being said, the 27c400 is a discontinued type of memory while the 27C2048 are still in production.

In other words, almost all Amigas require types of memory which are discontinued for their kickstart ROM chips, expect sockets U182-U183 in the A3000D...

That's a bummer!

It seems however that the chip 27C800 is still available in some places. Its pinout is the same as the 27C400 except it is a 42 pin chip that costs around 15$ apiece.

Of course, having twice the capacity of the 27C400, it has 42pins instead of 40 and it requires a bit of adaptation to be used as a 27C400 (minimal truly, 2 pins are added at one end of the chip, one extra address line and one NC).

It can also be used with a switch to carry TWO different kickstarts in an A2000 or A500. It could theoretically be used in pairs in an A1200/3000/4000 to carry FOUR different kickstarts selectable with two switches.

[da9000]

@mikolas:

Thank you for the explanation!
Could you tell us what revision is your A3000 motherboard?
Mine is (with the reversed silkscreen) is 9/03 @ 16Mhz.

@eslapion:
Interesting findings! Good research.
Pasting some links would be great ("From what I read, a ROM tower... allows the use of 27c400...").

[mikolas]

@da9000

Well my current mobo is rev 9/01 and has no ROM tower anymore :-). I think the older one was of major revision 7 or 8, not sure as it was quite a few years ago. I'm only certain it was not 9.