A500 trapdoor memory: free design

[SukkoPera]

Thanks @Mathesar! PM sent.

[zyonee]

I've ordered boards (latest revision) and RAM. As I've got an A500 rev 6a,i intend to make it 512k extra chip RAM and 1.5MB slow RAM.

I've already done the modifications to convert a regular trapdoor 512kb RAM expansion into chip mem. Wondering if I'll have to revert or change those modifications to achieve what I wrote earlier. The modifications I've done are on JP2 and JP7A.

[EzdineG]

Originally Posted by zyonee

I've ordered boards (latest revision) and RAM. As I've got an A500 rev 6a,i intend to make it 512k extra chip RAM and 1.5MB slow RAM.

I've already done the modifications to convert a regular trapdoor 512kb RAM expansion into chip mem. Wondering if I'll have to revert or change those modifications to achieve what I wrote earlier. The modifications I've done are on JP2 and JP7A.

Yes.

You’ll have to revert JP7A. JP2 will connect to the Gary board from its center pin, which can no longer be bridged to either of the other pins. You’ll then select the amount of chip RAM you use from jumpers on the Gary board.

[zyonee]

Originally Posted by EzdineG

Yes.

You’ll have to revert JP7A. JP2 will connect to the Gary board from its center pin, which can no longer be bridged to either of the other pins. You’ll then select the amount of chip RAM you use from jumpers on the Gary board.

Thank you!

[bruktmoped]

Random question: Is it possible to make another version of this pcb to make use of other chip types? It looks like these ram chips are harder to get than others? I have a big bag of old 72pin ram, but of course none of them has the correct chip

[zyonee]

I was looking at a Zydec MegaBoard (1MB slow RAM expansion that goes between the A500 and a regular 512 kb card). I found out that this one uses 74LS00 and 74LS139 logic chips for what I believe is the exact same operations as the F or HCT equivalents in this project. Didn't someone mention that 74LS may not be quick enough?

Picture here

Originally Posted by bruktmoped

Random question: Is it possible to make another version of this pcb to make use of other chip types? It looks like these ram chips are harder to get than others? I have a big bag of old 72pin ram, but of course none of them has the correct chip

I am looking into this, I would modify the board to use HY514260 or similar 256k x 16bit RAM (commonly found on old PCI S3 and Trident graphics cards)

My amiga rev 6a has 512 kb of ram. How many chips do I have to solder on this board to get 1.5mb in total.?
These chips are 1mx16 meaning they are 2mb so I am a bit confused here.

[EzdineG]

Originally Posted by sknipas

My amiga rev 6a has 512 kb of ram. How many chips do I have to solder on this board to get 1.5mb in total.?

These chips are 1mx16 meaning they are 2mb so I am a bit confused here.

Consider each chip you add to the board 512k of RAM. For a SYSTEM TOTAL of 1.5MB, you’d add two chips. To EXPAND BY 1.5MB, you’d add 3 chips. If you add 4 chips, you’d have a system total of 2.5MB.

Agnes can’t address any more than 512k out of each of these chips without more complex logic. This is why we’re not seeing 2MB out of a single chip.

Hope that clears this up for you.

That was helpful.
Thank you.

[Mathesar]

Originally Posted by zyonee

I was looking at a Zydec MegaBoard (1MB slow RAM expansion that goes between the A500 and a regular 512 kb card). I found out that this one uses 74LS00 and 74LS139 logic chips for what I believe is the exact same operations as the F or HCT equivalents in this project. Didn't someone mention that 74LS may not be quick enough?

Picture here

I measured some logic paths and found that the timing margin is very wide. So yeah, LS logic is probably fast enough. Nowadays, HCT logic is widely available and even faster than LS so that is what I have used.

[zyonee]

Originally Posted by Mathesar

I measured some logic paths and found that the timing margin is very wide. So yeah, LS logic is probably fast enough. Nowadays, HCT logic is widely available and even faster than LS so that is what I have used.

Alright, thanks! I've ordered HCT components anyway (and a batch of 74F00 as well before I found the HCT ones)

[SukkoPera]

So, I got Mathesar's boards (thanks!) and now I need to choose how to set them up. At least one of them will end up in an A500+ where, if I understand correctly, I don't have much choice, I can only get 1MB of extra chip RAM. No way to get more than that, right?

I will need two chips and the relevant caps, is that all?

Instructions for proper jumper settings are in posts 18 and 47, but they seem to contradict themselves pretty much, so what should I do in this regard?

Thanks in advance!

[demolition]

Originally Posted by SukkoPera

Instructions for proper jumper settings are in posts 18 and 47, but they seem to contradict themselves pretty much, so what should I do in this regard?

Put movable jumpers on the board like I have done - then you can always try out different combinations. You can't destroy anything by just trying out different jumper settings.

[PeteAU]

Originally Posted by SukkoPera

So, I got Mathesar's boards (thanks!) and now I need to choose how to set them up. At least one of them will end up in an A500+ where, if I understand correctly, I don't have much choice, I can only get 1MB of extra chip RAM. No way to get more than that, right?

I will need two chips and the relevant caps, is that all?

Instructions for proper jumper settings are in posts 18 and 47, but they seem to contradict themselves pretty much, so what should I do in this regard?

Thanks in advance!

Both my diagram or demolition's would work fine. I would solder only 2 chips though.

---

So has somebody combined this with a TF530? Supposedly 4.0-4.5 MB RAM is plenty for WHDLoad?

[EzdineG]

Originally Posted by PeteAU

So has somebody combined this with a TF530? Supposedly 4.0-4.5 MB RAM is plenty for WHDLoad?

I have.

It is enough for plenty of WHDLoad games if you keep to a light Workbench such as the 68k version of ClassicWB.

[alenppc]

Originally Posted by EzdineG

I have.

It is enough for plenty of WHDLoad games if you keep to a light Workbench such as the 68k version of ClassicWB.

Me too. The biggest drawback is falling back onto 16-bit ram once you run out of 32 bit ram which slows down some games considerably (e.g. Frontier, but to be honest that game doesn't really need WHDload since you can just copy the executable on the hard drive).

[Kato]

I am new here, that's why I warmly welcome everyone to the forum. I built A500 trap door B.4. Unfortunately, after installing the GARY adapter, I get a green screen. I built a second one and it is also the same problem. I used the rev. B.2 adapter and the memory has started. In SYSTEST it shows the correct value - Chip 1.0MB, Slow 1.5MB. It's probably not the fault of soldering, because then it would not work with rev. B.2 adapter. Can someone upload a picture of their Gary Adapter?
I used SN74F00D, SN74F74D, 74HCT139D.652 to build it. Why the new adapter has three 74F00s and one 74F74, and rev. B.2 only 74F00?

[Mq]

First: hello:-)

You must read previous posts in this thread to know why there are two or four-TTLs on the Gary adapter. Mathesar discovered faulty working two-TTLs adapter caused of Agnus DMA access to the RAM. Then he designed four-TTLs adapter which fixes that problems. This problems with old Gary adapter may not appear in memory test program. It occures when in some applications or games some specialise chips on motherboard use DMA memory acces.

Old two-TTLs Gary adapter works fine for slow memory configurations only, and don't works properly for chip memory configurations.

Second, use "direct memory scan", because "kickstart memory scan" sometimes shows wrong memory size (coused by wrong memory detection by kickstart if You set Gary adapter on wrong settings).

Unfortunately I don't know why You have green screen... Check connections...
And have You cut JP2 on motherboard?

[Kato]

Hey. Yes, I cut JP2. If you can check this PCB from my photo, maybe something bad was done in the factory while making the production ... although it's a small chance ...
It is rather on my side to find a problem. I will try to check everything again.
On the adapter of Gary rev. B2, I have a problem with running The Settlers (of course, we are talking about using all available memory all the time - on Amiga rev 6A)



This is on the title screen. Then after entering the game, everything is completely broken. I tested other games, it's normal there. For example, Pinball Dreams detects additional memory on the title screen. Can these disturbances in The Settlers be caused by damaged memory?
Maybe the problem lies in the integrated circuits that I used (?)

I forgot to ask if SYSTEST someday terminates memory testing? Recently, after a few hours, I finally turned off the Amiga - I did not want to leave her turned on for the night


Anyway, it's a great respect for the contribution for you and of course, first of all for PeteAU, Mathesar