EPROM type for Amiga 3000D Rev 9

[StompinSteve]

Hello,

There are several topics like these: https://eab.abime.net/showthread.php?t=49857 but they are too generic and confusing. The Rev.9 does not have a ROM-tower for example.

I cannot find a decisive, non-confusing answer, to the question of "which EPROM to use on the A3000 Rev. 9 Motherboard".

Can I use the AM27C400-120DC ?


(Disclaimer: I legally own the A3000 v3.1.4 ROM, but the ROM Chips I got from an official vendor do not work)

[StompinSteve]

I am going to answer my own question

In the paper manual that Hyperion Entertainments ships with their ROM Chips for the A3000D, it says the following:

For most A3000D units, the ROMs will go into the forward pair of ROM sockets.
These support the 27C400 ROM type.
The U180/ROM0 position will take the LO order of bits Kickstart chip, and the U181/ROM1 position will take the HI order of bits Kickstart chip.

The EPROM's notches must face towards the left side of the machine, away from the mouse/joystick connectors.

And to be complete, all of the above apply to the A3000T as well.

It also says that the U182 / U183 ROM Sockets in the A3000D are NOT compatible with 27C400 type devices. There should be nothing in those sockets on a Rev.9 Motherboard anyway.

Also, do NOT use the AM27C400-150DC chips one finds on eBay sometimes. They are 150ns units and are too slow. Use only the AM27C400-120DC (120ns) variant.

So there you have it. Question answered. I hope this helps someone in the future

[levo-ace]

Or faster , -100 -80 -70 -55 all are available and useable The -xxx denotes the speed , anything -120 ( 120ns ) or faster e.g -80 ( 80ns ) are useable , possibly better because of the faster access times.

These are from the M27C400-xxx range ( it does not have to be AMD ) from ST.

[Hedeon]

For the slow ones, isn't that what J150 and J151 is for? Genuine question?

[Jope]

Originally Posted by Hedeon

For the slow ones, isn't that what J150 and J151 is for? Genuine question?

Yep, I don't get it either. Almost any currently available 27c400 EPROM should suffice even at the tightest settings.

Of course it is very probable that most of the ROMs currently sold as AM27c400 are remarked, so there may be some experimentation required.

[SpeedGeek]

Originally Posted by StompinSteve

Also, do NOT use the AM27C400-150DC chips one finds on eBay sometimes. They are 150ns units and are too slow. Use only the AM27C400-120DC (120ns) variant.

I've been using 150ns units with the shortest possible ROM timing for many years now.

So, some people just don't understand how the ROM timing works:

http://www.l8r.net/technical/t-3000-jumpers.shtml

[StompinSteve]

Thanks SpeedGeek. I was not even aware that existed.
I have been warned by several people to stay clear of anything above 120ns so that has become my truth

[Jope]

The A4000 doesn't allow you to set timings below 160ns either. :-)

Based on my experience, there will always be some unburnable EPROMs when buying these 27c400 chips from China. Also I have noticed when buying a bigger batch, that the dies behind the quartz window come in various shapes and sizes, yet they all have identical AMD printing on the package. "Curious." :-)

[StompinSteve]

@ Jope: yeah I noticed that too. Those "China" versions are also suspiciously cheap... I bought a couple from European vendors. First of all, those are never "new" and never "cheap" but the Chinese versions (almost always knock-offs) often are (with date-marks saying 1997 etc....).

Personally I steer clear of China. They reverse-engineer, steal, copy, rob and rip like there is no tomorrow. I trust them as far as I can throw them...