A500 trapdoor memory: free design

[alenppc]

You can't have $C00000 ram on the 500+?

[demolition]

Originally Posted by alenppc

You can't have $C00000 ram on the 500+?

Not using the trapdoor connector, unless you do some patching of the MB.

[springycz]

OK, so it only makes things easier. I already have the fast RAM on GVP A530.
Only question left is whether some of the chips I listed in my previous post will work in this expansion? All should be 1M x 16 just like those used in the first post.

[demolition]

Originally Posted by springycz

I found several simms containing 42 pin chips that are supposedly 1Mx16, namely:
HY4181164B, KM416C1200AJ-7, TMS418160DZ, AS4C1M165S-60JC, and HM5118160-AJ7
Will anyone of these work with this expansion?

I found some datasheets: KM416C1200, TMS418160, AS4C1M165, HM5118160. Did not find any for HY4181164B.

They are all 5v 1Mx16bit DRAM with FPM and the same pinout, so they should all be compatible as far as I can see.

Some of them are 60ns, some are 70ns. Not sure whether the speed matters, but I guess that 70ns is good enough for this.

[springycz]

Thank you!

[Mq]

Hi there. I tested some chips 60ns and 70ns. You can use both of them, and it doesn't matter even if You mix 60ns and 70ns chips in one extension. If chips are good, then they works for me even if I use four diffrent chips and with diffrent access time.

Hi, first of all thank you guys for your work, Amiga is a community that have so little diy stuff and I appreciate people effort to release free things, thanks again.

I'm from brazil and bought some pcbs from elecrow to build 2 expansions for both my A500s. So I have tons of old pc parts and found many edo simms, but it seems that all of them have 2Mx16bit chips like TMS418169DZ. I also found a couple of simms that have hy5118164b which in the datasheet (http://www.ic72.com/pdf_file/h/11436.pdf) says it's 1M, but the simm recognize as 2MB in my test 486, since it has only 4 chips I assume that they are 2M. All my simms that use 16bit chips have 4 on it and are 2MB.

Now I got a little confused abou which chips I can use tu build the expansion board, does the 2M chips work?

[demolition]

Originally Posted by instorm

I'm from brazil and bought some pcbs from elecrow to build 2 expansions for both my A500s. So I have tons of old pc parts and found many edo simms, but it seems that all of them have 2Mx16bit chips like TMS418169DZ. I also found a couple of simms that have hy5118164b which in the datasheet (http://www.ic72.com/pdf_file/h/11436.pdf) says it's 1M, but the simm recognize as 2MB in my test 486, since it has only 4 chips I assume that they are 2M. All my simms that use 16bit chips have 4 on it and are 2MB.

Now I got a little confused abou which chips I can use tu build the expansion board, does the 2M chips work?

TMS418169 are 1Mx16 and so is HY5118164B. These are exactly the chips you need to build this expansion. I think as long as the pinout fits the footprints (SOJ 42), they are likely suitable.

From original post:

Originally Posted by PeteAU

Technically, the chips are called SOJ42, 1M x 16. You can identify them visually, they are the bigger/longer chips. If you count 21 pins on one side (42 total), it's a winner.

[katarakt]

I asked the same some weeks ago. 2Mx16 = 1Mx16 if they have 21 pins on one side, i think so because this is what the nice experts here said? Btw...most manufacturer call these chips 2Mx16 in their datasheet and not 1Mx16. Why? I don't know. Still a bit confusing. Can someone tell the difference between 2Mx16 SOJ42 and 1Mx16 SOJ42 ?

Oh, Mathesar...have you received the new pcb's ?

[Mq]

It's simple mathematics. 1Mx16bit=16Mbit=2MB because 1byte=8bits. So same chips can be named 1Mx16bit or 2MB or else 16Mbit. And important: lowercase "b" means bit, and uppercase "B" means byte.

In electronics it is more often said about bits not bytes because at the same time it determines organisation of memory which is just as important as overall size of memory.

[demolition]

Do you have an example of a datasheet that says 2Mx16 with a SOJ42 pinout? I am unable to find one..

If I go to http://www.mouser.dk/Semiconductors/...RAM/_/N-4bzp3/ for example and select SOJ 42 and 16 bit data bus width, I only get 1Mx16 chips.

[katarakt]

Thanks Mq666, i thought something like that.

@demolition
No, i haven't saved the spec sheets. I've done some research for the rams i found on ebay a while ago and some of them called 2MBx16 and SOJ42. That's why i've asked some weeks ago.

[Mq]

Perhaps someone has used an acronym or thinking shortcut and wrote 2MB as 2 megabytes of size and x16 as 16 bits organisation. But this is a misnomer. Properly should be 2MB or 1Mx16b or 16Mb. Anyway it was probably the same chips, but you must check it allways in datasheets.

[springycz]

Hello, I have an additional question regarding this trapdoor memory.
I have an A500 with rev. 8A motherboard inside. It´s basically the same motherboard like in A500+s though it has just 0.5MB of chip RAM and a KS1.3 installed, and it´s also missing the RTC circuitry. The rest of chips are the same like on the A500+ motherboard including ECS Denise and Agnus.
I just found Kippers2k thread where he managed to convert this board into A500+ (without RTC which he had on trapdoor expansion).
What I would like to ask is whether this particular trapdoor memory is able to provide 1.5MB of chip RAM so I do not need to install the additional 0.5MB of chip RAM on the motherboard. It would be nice if it works as an all in one the onboard 0.5MB and the additional 1MB trapdoor ram.

[appiah4]

I have the prototype board of this expansion card and I used an AS4C1M16E5-60JC 1Mx16 module on it.

What I don't understand is, why do we use a 2MB module on on a 512K expansion? Can anyone tell me why it's not a 512Kx8 or 256Kx16 module instead?

[demolition]

Originally Posted by appiah4

What I don't understand is, why do we use a 2MB module on on a 512K expansion? Can anyone tell me why it's not a 512Kx8 or 256Kx16 module instead?

Because those 1Mx16 chips were readily available by the author of the expansion?

[appiah4]

Originally Posted by demolition

Because those 1Mx16 chips were readily available by the author of the expansion?

Ok it's not a hardware requirement of some kind then, that's all I wanted to know

[demolition]

I don't think so.

16 bit width is useful as you only need one chip to get the basic 512kB expansion, but other than that, he could probably have designed it using 256k x 16 chips if he had those available. Not sure how commonly they were on PC memory modules?

Originally Posted by demolition

TMS418169 are 1Mx16 and so is HY5118164B. These are exactly the chips you need to build this expansion. I think as long as the pinout fits the footprints (SOJ 42), they are likely suitable.

From original post:

Thank you for the quick answer, which makes me very happy since now i have tons of chips to build my boards

[katarakt]

About the RTC 62421 ...does it matter if 62421A or 62421B ? What is the difference ?

And about 74F74 ...i found some but what is the difference between 74F74 and 74F74SJ ?? Both ok?