14Mhz Accelerator

[Samurai_Crow]

Perhaps bypassing the clock doubler circuit but leaving the fast RAM active would be better. Can that be done on a board with so few layers?

[Mathesar]

bypassing the clock doubler also means bypassing the as/dtack and e clock logic. That would require quite a few extra multiplexer chips. Just disabling fast ram is quite easy to do and although not perfect, would make the machine almost stock.

I have been thinking a bit about the purpose of this little accelerator. I mean, the accelerator is fun to build but what to do with it in an A500?
I came to the conclusion that this accelerator is useful for those who want to keep a stock A500 for old-school games but sometimes want a bit more oomph for the more demanding games (dune II, upcoming Dread, Elite, etc). Then it is indeed important to be able to switch back.

What if we could disable the fast ram by holding ctrl-amiga-amiga for longer than usual.... (does anyone know the 555? )

[hooverphonique]

Originally Posted by Mathesar

What if we could disable the fast ram by holding ctrl-amiga-amiga for longer than usual.... (does anyone know the 555? )

I actually thought about this (even the 555 ;-) when writing my previous comment, but didn't want to suggest you complicating the circuit, but now you suggested it yourself...
The question then becomes if the long reset is a toggle operation (persistent until power cycle), so you don't need to long reset for each reset to keep the accelerator "off".



I think "just" disabling the ram sounds practical.

[keithamiga1200]

Awesome

[Mathesar]

Originally Posted by hooverphonique

I actually thought about this (even the 555 ;-) when writing my previous comment, but didn't want to suggest you complicating the circuit, but now you suggested it yourself...
The question then becomes if the long reset is a toggle operation (persistent until power cycle), so you don't need to long reset for each reset to keep the accelerator "off".



I think "just" disabling the ram sounds practical.

Making the action persistant until power cycle is more practical indeed but also needs a few more components. What about this circuit:

Just the 555, an electrolytic cap, a resistor and a spare inverter.
This circuit will enable the ram upon a normal ctrl-amiga-amiga or powerup reset. But it will disable the ram when you hold the keys down for more than 5 seconds.
I just have to check whether the reset signal from the Amiga goes all the way to 5V.

LTSpice file here: ram_disable_reset_timer.zip

[Mathesar]

Quick update:
Things were busy lately so progress was slow. I have finished the layout for the revised board though. I will order some this week. The new design contains the 555 circuit to disable the RAM by holding ctrl-amiga-amiga down for more than 5 seconds.

[Mathesar]

Oke, boards are ordered at https://aisler.net (highly recommended when you're located in EU btw).
Will arrive in 2..3 weeks time as I chose the "budget" option. Won't have much time to work on it before that anyway.

This is what it will look like:


I will release it under CERN-OHL-S which is somewhat the hardware equivalent of GPL. This means anyone can do with it whatever they want as long as they open source any changes.

[Amarok]

After a very long break from anything Amiga related I now started following some of the (IMHO) most exciting Amiga HW projects, so just wanted to thank everyone for the effort! (Regardless of the HW project he's working on).

Looking forward to the 14MHz accelerator since I have a few MC68HC000FN20 which I haven't tested yet (bought on eBay from China) and they should hopefully work in the board (once I have one ). My HW knowledge is very limited, but AFAIK a 20MHz CPU should run fine on 14MHz, since 20MHz is the top limit(?)

[Mathesar]

Originally Posted by Amarok

My HW knowledge is very limited, but AFAIK a 20MHz CPU should run fine on 14MHz, since 20MHz is the top limit(?)

Yes, it will run fine. In fact I am also using 20MHz MC68HC000FN20.
I've also tested an MC68010FN12 and that also worked. The latter pushed the SysInfo rating close the 3 times faster than a standard A500

[Mathesar]

Quick update:
Boards came in. I assembled one and.... didn't boot . Turned out I made a thinking error in this revision when I replaced an '112 JK flipflop with an '74 D latch. Luckily I could fix it by patching the _Q output to the asynchronous _SET input. I was very lucky here that the behaviour when both the asynchronous set and asynchronous reset are asserted was exactly what was needed. Close call! Otherwise I would have to revise the circuit again. Now it works with only a small patch! The release version (which will have the patch) will thus now be rev2.2..

[nikosidis]

Originally Posted by Mathesar

Quick update:
Boards came in. I assembled one and.... didn't boot . Turned out I made a thinking error in this revision when I replaced an '112 JK flipflop with an '74 D latch. Luckily I could fix it by patching the _Q output to the asynchronous _SET input. I was very lucky here that the behaviour when both the asynchronous set and asynchronous reset are asserted was exactly what was needed. Close call! Otherwise I would have to revise the circuit again. Now it works with only a small patch! The release version (which will have the patch) will thus now be rev2.2..

Will you sell this hardware?
I would like to buy one

[Amarok]

That's so good to hear! My fav Amiga mod now finally in production version :-) I'm very interested in this board, either gonna order a new PCB myself and all necessary parts as well (without the CPU which I already have) and then some soldering work, or - should you offer a complete set (soldered or not) without the CPU I would be interested too (shipping inside of EU should be fine and cheap).

[nikosidis]

Originally Posted by Amarok

That's so good to hear! My fav Amiga mod now finally in production version :-) I'm very interested in this board, either gonna order a new PCB myself and all necessary parts as well (without the CPU which I already have) and then some soldering work, or - should you offer a complete set (soldered or not) without the CPU I would be interested too (shipping inside of EU should be fine and cheap).

I would also like to buy complete set without CPU if possible.
This project is perfect for my needs

I have done the chip mod to my A500 so it now got 1MB chip.
I also changed the ROM to 2.x

I have read the whole thread and the option to disable fast is smart

[keithamiga1200]

Outstanding piece of development It's great to see stuff like this, where one can easily assemble at home, without needing to learn programming or anything. I do hate soldering 805 capacitors/resistors But design needs must


IDE on Reversion 2?

[Mathesar]

Another update:

All systems working!

I have now fully assembled one prototype and everything is working as intended, even the "disable ram by holding ctrl-amiga-amiga for more than 5 6 seconds" works. Although the exact amount of seconds may vary .

Here is picture of the complete build installed in my A500:


And here is how the board looks like if one just builds the bare "accelerator" as it was intended in 1990-something:


Like said before, I need to make one small fix in the design that will bump the version number to V2.2. If hope to release everything coming weekend.

[Mathesar]

Originally Posted by nikosidis

I would also like to buy complete set without CPU if possible.
This project is perfect for my needs

I have done the chip mod to my A500 so it now got 1MB chip.
I also changed the ROM to 2.x

I have read the whole thread and the option to disable fast is smart

I usually do not sell any boards and/or parts unless I have some left. However this project was tougher that anticipated so I do not have anything left this time. I will just release this as open source hardware to the community for anyone to build. Otoh, the parts should be easy to obtain, even with the current shortage going on.

[Mathesar]

Originally Posted by keithamiga1200

Outstanding piece of development It's great to see stuff like this, where one can easily assemble at home, without needing to learn programming or anything. I do hate soldering 805 capacitors/resistors But design needs must


IDE on Reversion 2?

Yeah, the fact that it uses no programmable logic makes it fun eh? And yes, 0805 caps and resistors are small. I use a 5X loupe .
But, one could redo the design in through hole? It would just get bigger!

Oh, and IDE is soooo 1990. SPI/SD-card is the way to go in the 21st century

[AJCopland]

Congratulation Mathesar that's awesome work!

[Mathesar]

Released!

http://eab.abime.net/showthread.php?...12#post1493912

[TEG]

Congratulation.

Can you post a SysInfo screenshot?