Easily replace st stf/m mega st ram with a 4/8mb simm

[simbo]

This is the start of a guide I am still waiting for a few things in the post tomorrow, I hope.
This Guide shows how to expand an stf/m to 4 MB using a 74pin simm,
i would use a 4mb simm i find using some types of 8mb simm or 16 youll only get 512k
when you add the switch for 1mb if you intend too something to do with RAS1 i need to experiment a little
unless someone has cured this issue in the past???
the first picture is of another stfm I have has the rom sockets under the psu,
and two rows of ram I'll do this one last as I'll make a separate guide hopefully;
with help of photo materal of other's as they do this also.
I have changed it's memory buffers already.
I feel this is a needed step to interface to the simm correctly, and aid in stopping any packet loss.

I'll expand the picture guide as I complete these steps on these two st machines of the same rev 1.1 board
one stf one stfm one has 74ls11 fitted to the roms the other not but will have as I get one.
both I'll add flash tos chips to as it's a great project for more than fun.
so I'll cleaned out its pin holes ready for the chips {Just us an LS type here is fine I feel.}.

First you need a few bits and tools:

techie_alisons memory upgrade guide

sharp side cutters.
solder irom 25watt for removing and if you have it a 17 watt for fitting using a 25 watt with care is enough.
solder 22swg lead/tin/flux core.
pair of small radio pliers.
inspection mag glass.
some twezers long and thin but stirdy.


memory and hookup bits:
A non right angle simm socket 72pin. {See links in hardware section I posted about memory and stuff and where to buy it cheap.}
A 72pin 4 or 8mb fastpage 80 ns or better simm. {Again see the links in the hardware section to a cheap ebay seller.
http://www.atari-forum.com/viewtopic.ph ... 70#p152970}

1 meter of flat gray or multicoloured ribbon cable. {I got 2m for £2 on ebay last week free post.}
1 set of tubes of epoxy glue like araldite or others. {you'll find cheaper types not as good.}
1 tube of super glue. {Use locktight stuff its better than the cheap tubes. }
{Total cost is about £11 for all of these bits.}
1 bit of wet and dry sand paper to make a key on the sim sockets glue surface.

memory buffers:
2X74HC244 {you can use F types or HCT here ACT types is'nt needed}
2X74HC373 {again you can use F types or HCT if you like}

So I've already replaced, as youll see below both buffer ics, in both machines.
Also I've take off the older ram that lives under the psu.

Also the small yellow bypass capacitors that are on the psu rail of each mem chip,
this makes more space for the simm socket to glue too.

I'll post more as I go so check back and grab the bits.

IMG_0561.JPG

IMG_0563.JPG

IMG_0565.JPG

IMG_0568.JPG

IMG_0580.JPG

[simbo]

todays rev 1.1 machine

note the use of pin strips on the buffer ic needed pins

finaly triple check your work
see alisons memory upgrade details on her site
for more details

http://www.logicsays.com/atari/

i do however also replace the buffer ic's as ttl 74LS logic is not fully complient with 72 pin simms dram chips gates

[simbo]

bits from ebay still avalible

http://cgi.ebay.co.uk/Ribbon-Cable-10-w ... :MEBDIX:IT
http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... :MEBDIX:IT
http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... :MEBDIX:IT

[simbo]

ive since fitted some 4mb 8 chip 70ns simms to all moded machines

and all is fine 4mb and 1mb on switch
no issues

the st menus respond faster
the two machine moded with tos1.04 and simm
and also the memory buffers are great

much sharper for sure!!!

concider replacing the memory buffers also
although its nearly as good without replacement

and i havent noticed any breaks in use,... with 74hc types used,,,

[Nikolas]

replacing with HC thats 74HC memory buffers it give me faster st machine? less data loss within st?

In my expirience 74LS for 74HC is improved data trafic, more acurett and better stability

[simbo]

you dont have to change them i just do i find in practice there is little change
only the current the machine uses changes

ls or hc/t is just as good
however i use 74HCT myself when i can find them
hc type high speed cmos i agree isnt the best its just what i had
hct is far better

or leave them alone and just add the jumpers to there pins


it just makes the simm more compatable in terms of voltage levels TTL / CMOSTTL to the mmu

[sim-os]

hi simbo,nice guide ,have a some questions..
on ST board has already 74XX chips?,and if yes.. is important to change the default 74XX chips with others? (i have a lot 74LS.. )
on alison site guide i thing she is do-not use the connection on MMU chip [pin64]?
at last your pic,s is nice but no so helpful,maybe one more analytic connection diagram is more useful ,(your cable have multi colors lines,but is double..)

[Anemos]

@simbo,excellent mod!
What,s on gaming? dos games or game then need 1 or 4 mb?
If you can make one list with pins directions-connection, Ram to Atari board ,that gones very helpful .

[simbo]

hi

adding the switch is simple
there is normaly mad 1-8 you need to use mad {memory address} 9 it is not normaly connected
on the glue chip is st machines

you add a 33 ohm resistor and a single pole switch
switch one way it connects and yields 4MB addressing
switch the other and 1MB normal memory level is attained for some games as you know dont like 4mb


as for a list of pins if you read techie_alisons guide they are there
youll note some address pins need to connect together

i dont suppose she will mind if its here if she does im sure she can just delete it

[499]

simbo, can you better show which wires connect to which pins on the memory buffers? Maybe show all connections to the motherboard in one list?
Thanks!

[brownb2]

Can somebody restore the photos on this page? I was looking to possibly do this upgrade but not without photos!

[Dal]

I'm on it...

[Dal]

BOOM! They are back.

Sorry it took a while.

[Giants]

Blup

Several years after

I find some errors in the guide v1.02 and v1.03

After the SImm description, I see
>*40 connections to be made
But I found only 39
(D0 to D7) : 8
(D8 to D15) : 8
(RAS and CAS) : 6
(A0 to A9) : 10
WE : 1
GND and +5V : 6
(8 + 8 + 9 +10 +1 + 6) = 39
I missed one ?

And, this is very important. In the section 6 (connecting your SIMM socket to ..)
I See on your document :
R59 > RAS0
R60 > CAS0L
R61 > CAS1L ---> I think it's wrong but the good connexion is : R61 > CAS0H isn't it ?
...
R71 > CAS1H
R72 > CAS1L
R73 > RAS1

But, for even with modification ,it's don't work on my STF, maybe my memory is not good..
as I have no SIMM 72 pin connectors, I connect directly the SIMM it's complicated to test other SIMM memory.

UPDATE : Hoo, I See it's my first post here, sorry about that.
I just discover maybe (i'm sure in fact), I forget to Link in my SIMM memory a lot of pin like ::
Pin2 and Pin3 (D0 and D16)
Pin4 and Pin5 (D1 and D17)
...

For me, all this pin (D16, D17...)is connect to nothing so... -_-'