A500 trapdoor memory: free design

[demolition]

Originally Posted by emufan

can you tell me where i may find this memory test tool/module?

I'm guessing it is a custom kickstart ROM?

[emufan]

Originally Posted by demolition

I'm guessing it is a custom kickstart ROM?

thats my impression too, maybe Pete made it on his own

[PeteAU]

Originally Posted by emufan

can you tell me where i may find this memory test tool/module?

That's keirf's systest: https://github.com/keirf/Amiga-Stuff
You can download a bootable ADF there, it's good stuff for h/w testing.

[emufan]

Originally Posted by PeteAU

That's keirf's systest: https://github.com/keirf/Amiga-Stuff
You can download a bootable ADF there, it's good stuff for h/w testing.

ah, cool. thanks. i know keirf by his disk-tools, but didn't knew about the amiga-stuff project
kudos for your hardware project - really impressive, what you guys can do between breakfast and lunch

[dalek]

wow cool - thanks for releasing the eagle files.

I've got a bunch of those connectors and have been meaning to make a A501 replacement board that will take the old style DIP chips from trapdoor expansions that suffered bad battery leaks (I have a few!). This will be a good start!

[PeteAU]

Hi,

Anybody receive the boards I sent yet? Might be too soon, they should start arriving next week.

So, I've taken it a step further and made a prototype gary-adapter.
Now I've put 3 memory chips on the original board, and the adapter should allow them to be mapped into the appropriate place in memory.

And... tadaaa.. it works. Look at all that extra slow RAM, party like it's 1987!

Unfortunately I can't get the 3rd chip working, I suspect it's because kickstart 1.2 doesn't allow it and I need to get a 1.3 kick rom.

This prototype is no good for 1MB chip RAM, but I see what I did wrong and could make it work for 1MB chip in the future.

If somebody wants to replicate this, it's pretty easy and no expensive parts needed.

Cheers,

[appiah4]

Originally Posted by PeteAU

Hi,

Anybody receive the boards I sent yet? Might be too soon, they should start arriving next week.

So, I've taken it a step further and made a prototype gary-adapter.
Now I've put 3 memory chips on the original board, and the adapter should allow them to be mapped into the appropriate place in memory.

And... tadaaa.. it works. Look at all that extra slow RAM, party like it's 1987!

Unfortunately I can't get the 3rd chip working, I suspect it's because kickstart 1.2 doesn't allow it and I need to get a 1.3 kick rom.

This prototype is no good for 1MB chip RAM, but I see what I did wrong and could make it work for 1MB chip in the future.

If somebody wants to replicate this, it's pretty easy and no expensive parts needed.

Cheers,

This works on KS1.3 machines with 512K chipram? Like mine?

Haven't received mine in the mail yet.. But very interested in following up with this (though I assume it would not play ball with my ACA500plus..)

[radfoo]

Originally Posted by PeteAU

Hi,

Anybody receive the boards I sent yet? Might be too soon, they should start arriving next week.

Well done, looks good! Not received mine yet, looking forward to having a play. Shame about the 1Mb chip Ram, what was the problem?

Wow, absolutely awesome!

It's my first post here and this forum is great.
Not only did I find exactly what I was looking for in scart cable thread, but also this post was exactly what I was hoping for, thanks a lot!!!

I've had my A500 for many years, but never tinkered with it until recently.. the floppy drive decided it no longer wanted to eat disks.. and oh well, I ordered a gotek + programmer to get that up and running hopefully next week.

Coincidentally I also was offered several A500's in a package deal with some C64's that I was trying to buy and it was an offer I couldn't refuse.. so I popped them open yesterday and noticed no memory expansion.. oh dear.. better browse the web and now I'm here.

Seeing as I am only after creating a similar setup as my own machine (+512) I will gladly use the sch/brd many thanks!

A few questions though, hope you don't mind;

1. I noticed you blocked one specific field "more than 512K" -> am I assuming correct that all other parts except for this block are to be populated on the board? (so for example do I populate C4, C5, C6 etc)

2. Googling the RTC, I saw elsewhere that when populating a RTC on the expansion, it might require some adjustments to a mainboard to disable to onboard RTC. That applies here too correct?

3. My own machine (and most I remember from back in the day) had a on/off switch (with or without a LED drilled into the top of the case) to switch between 512 and 1, is there a way of adding that to this design?
(i have to be honest here, I don't ever recall turning mine off, so I don't even know if that is necessary)

Many thanks,
Tim

[PeteAU]

Originally Posted by radfoo

Well done, looks good! Not received mine yet, looking forward to having a play. Shame about the 1Mb chip Ram, what was the problem?

I just didn't put enough thought into the 1MB chip logic. It should be fixable on the gary adapter only, the original main board is OK.

Originally Posted by appiah4

This works on KS1.3 machines with 512K chipram? Like mine?

Haven't received mine in the mail yet.. But very interested in following up with this (though I assume it would not play ball with my ACA500plus..)

Sure. It shouldn't interfere with fastram.

Originally Posted by TimHarris

Wow, absolutely awesome!

It's my first post here and this forum is great.
Not only did I find exactly what I was looking for in scart cable thread, but also this post was exactly what I was hoping for, thanks a lot!!!

I've had my A500 for many years, but never tinkered with it until recently.. the floppy drive decided it no longer wanted to eat disks.. and oh well, I ordered a gotek + programmer to get that up and running hopefully next week.

Coincidentally I also was offered several A500's in a package deal with some C64's that I was trying to buy and it was an offer I couldn't refuse.. so I popped them open yesterday and noticed no memory expansion.. oh dear.. better browse the web and now I'm here.

Seeing as I am only after creating a similar setup as my own machine (+512) I will gladly use the sch/brd many thanks!

A few questions though, hope you don't mind;

1. I noticed you blocked one specific field "more than 512K" -> am I assuming correct that all other parts except for this block are to be populated on the board? (so for example do I populate C4, C5, C6 etc)

2. Googling the RTC, I saw elsewhere that when populating a RTC on the expansion, it might require some adjustments to a mainboard to disable to onboard RTC. That applies here too correct?

3. My own machine (and most I remember from back in the day) had a on/off switch (with or without a LED drilled into the top of the case) to switch between 512 and 1, is there a way of adding that to this design?
(i have to be honest here, I don't ever recall turning mine off, so I don't even know if that is necessary)

Many thanks,
Tim

No worries.

1. Yes, you don't need the 74F139 and don't need U2, U3. Also C4-C6 is for the extra memory chips, so you don't need them either. I think the total parts list for 512K is:

CTX: 2x28 2.54mm right-angle female header (or buy 2x40 and cut it).
U1: SOJ42 1x16M DRAM
C1,C2,C3: 100nF X7R 0805 capacitors (maybe one is enough)

2. Only needed for A500+ (the "plus")

3. There's an enable jumper on the board, which could be wires and a switch if wanted. But don't drill holes in your case

I've still got 1 spare PCB if you want to pay the postage.

Cheers,

Oh really? that would be awesome Pete

I will drop you a pm, thanks!

Just a remark regarding the DRAM chips: 256k x 16 (4Mbit) are sufficient to build a 2MB expansion with 4 chips. Examples are IS41C16256 or M11B416256A. They are available in 40pin SOJ packages.

My idea for the Gary adaptor: If you make Gary 'see' $C00000 by separating it from the address bus with logic chips, you can expect it to generate the same signals every time memory locations are accessed where the 2MByte expansion resides. For that you'd only need 4 address pins and maybe a clock signal to avoid glitches.

[PeteAU]

Originally Posted by _-cp-_

Just a remark regarding the DRAM chips: 256k x 16 (4Mbit) are sufficient to build a 2MB expansion with 4 chips. Examples are IS41C16256 or M11B416256A. They are available in 40pin SOJ packages.

Sure, I just tried to recycle what's on-hand and plentiful. You can buy them, but not many people will have the 40pin in their box of old junk.

Originally Posted by _-cp-_

My idea for the Gary adaptor: If you make Gary 'see' $C00000 by separating it from the address bus with logic chips, you can expect it to generate the same signals every time memory locations are accessed where the 2MByte expansion resides. For that you'd only need 4 address pins and maybe a clock signal to avoid glitches.

That's all fine in theory, but how many logic gates can you crunch that down to? You also need to map the first 512K into $08,000 for chip RAM, then the rest at $C0,0000. Or all of it at $C0,0000 for half meg Agnus.

I had some idea about using just 1 DRAM chip to create the whole 2.0 MB expansion. But the logic to make the refresh cycles work is difficult (detect both RAS0/RAS1 being asserted, generate an alternating DRA9 etc.). Tricky stuff.

[demolition]

Originally Posted by PeteAU

Sure, I just tried to recycle what's on-hand and plentiful. You can buy them, but not many people will have the 40pin in their box of old junk.

That's all fine in theory, but how many logic gates can you crunch that down to? You also need to map the first 512K into $08,000 for chip RAM, then the rest at $C0,0000. Or all of it at $C0,0000 for half meg Agnus.

I had some idea about using just 1 DRAM chip to create the whole 2.0 MB expansion. But the logic to make the refresh cycles work is difficult (detect both RAS0/RAS1 being asserted, generate an alternating DRA9 etc.). Tricky stuff.

I had a bunch of unused 40-pin RAMs in my junk box that I thought I could use until I counted the pins.
But I also had some old RAM modules with those 42 pin ICs on it so it should be good anyway.

For the digital logic, it should be simple enough if you venture into CPLD/PAL/etc territory, but then it will throw off many regular users who do not have the equipment to program these chips. But if someone is making a bunch of PCBs, they could also supply a pre-programmed IC along with it.

[appiah4]

I think I'll get the board in the mail today. The chips should arrive shortly as well. If I can get the chip soldered on right, I'll then try to reproduce the RTC clock components install. This will be my first time soldering electronics, I hope I don't butcher your board PeteAU..

[PeteAU]

Originally Posted by appiah4

I think I'll get the board in the mail today. The chips should arrive shortly as well. If I can get the chip soldered on right, I'll then try to reproduce the RTC clock components install. This will be my first time soldering electronics, I hope I don't butcher your board PeteAU..

First time soldering and you jump straight into a surface mount RAM chip? A bit scary

Originally Posted by demolition

I had a bunch of unused 40-pin RAMs in my junk box that I thought I could use until I counted the pins.
But I also had some old RAM modules with those 42 pin ICs on it so it should be good anyway.

For the digital logic, it should be simple enough if you venture into CPLD/PAL/etc territory, but then it will throw off many regular users who do not have the equipment to program these chips. But if someone is making a bunch of PCBs, they could also supply a pre-programmed IC along with it.

Yeah, good point, a little CPLD could do the job. I guess somebody else can edit my board and make a 40pin variant if they want.

---

So it turns out 1.2 kickstart cannot support 1.5MB slow ram and just yellow-screens. But no problem with 1.3 or 3.1, I wonder why. Now I just need a 1MB Agnus to finish it off.

[appiah4]

Originally Posted by PeteAU

First time soldering and you jump straight into a surface mount RAM chip? A bit scary

I'll probably ask someone who knows how to handle soldering iron/paste to give me a hand with it Could you please confirm whether C2/3 are optional or mandatory for 512K expansion with RTC? Your prototype seems to have only C1 but later you mentioned populating C1/2/3 for 512K so I'm kind of confused. Also, 100nF X7R 0805 caps for these right?

[radfoo]

Originally Posted by PeteAU

Hi,

Anybody receive the boards I sent yet? Might be too soon, they should start arriving next week.

Mine arrived today, thanks!

Going to have a play in a bit (assuming I can find where I left the connectors). Will do 512kb, fingers crossed. Was a bit confused by the last 1mb comments you made, will it definitely not work or was that just in relation to the gary board?

EDIT:
Soldering went better than expected, thought i'd mess up the DRAM chip but that went okay in the end, stupidly broke a trace on one of the pin headers but managed to fix (luckily was able to blob 2 pins together). Unfortunately did not work and run out of time for today, only put the capacitor in C1 and have no connector on the clock end of the PCB, wondered if the through holes need connecting even if the circuit and last 16pin connector isn't used? Should there by any jumpers set on 512kb? Anyway, end result is the 500 keeps rebooting, never gets to kickstart. Will try again tomorrow :-)

EDIT EDIT:
Could not leave it, lol. Turns out that broken trace was never broken, had to remove the connector and put another one in, system now boots but I don't have any extra RAM.

[PeteAU]

Originally Posted by radfoo

Mine arrived today, thanks!

Going to have a play in a bit (assuming I can find where I left the connectors). Will do 512kb, fingers crossed. Was a bit confused by the last 1mb comments you made, will it definitely not work or was that just in relation to the gary board?

EDIT:
Soldering went better than expected, thought i'd mess up the DRAM chip but that went okay in the end, stupidly broke a trace on one of the pin headers but managed to fix (luckily was able to blob 2 pins together). Unfortunately did not work and run out of time for today, only put the capacitor in C1 and have no connector on the clock end of the PCB, wondered if the through holes need connecting even if the circuit and last 16pin connector isn't used? Should there by any jumpers set on 512kb? Anyway, end result is the 500 keeps rebooting, never gets to kickstart. Will try again tomorrow :-)

EDIT EDIT:
Could not leave it, lol. Turns out that broken trace was never broken, had to remove the connector and put another one in, system now boots but I don't have any extra RAM.

Which last 1mb comment? It'll work fine as 512KB in almost all situations.

The last 16 pins don't need any solder.

Post a pic, maybe we can spot the error. How did you remove the connector? That sounds really hard/impossible/dangerous.

Does your mobo have JP2 changed to 1MB chip? If so, you need to cut the ENABLE jumper on the memory board. This jumper really means: "enable expansion RAM at $C0", but for CHIP, you don't want that.

[radfoo]

Originally Posted by PeteAU

Which last 1mb comment? It'll work fine as 512KB in almost all situations.

Yeah, just working on it as 512kb at the moment. I meant in relation to having 1mb chip expansion on an A500 Plus

Post a pic, maybe we can spot the error. How did you remove the connector? That sounds really hard/impossible/dangerous.

I mean the connector on the expansion PCB not the A500, was easy to remove and put another one was just the first 20 pins. Think it was pin 20 I ended up connecting up to ground, if its nothing obvious (jumpers etc.) then I suspect I damaged the RAM with that mistake.

Does your mobo have JP2 changed to 1MB chip? If so, you need to cut the ENABLE jumper on the memory board. This jumper really means: "enable expansion RAM at $C0", but for CHIP, you don't want that.

I'm using it on an A500 Plus, so expecting 1.5mb chip ram.

Thanks.