ciceron@chorus.fr (Carrez Stephane) (06/06/90)
I was fed up with seing messages like "out of memory", "not
enough memory" with my Mega ST2. Ok, this happens under Minix (sorry,
I never use GEM). Then I decided to add 2Mb of memory to get a Mega ST4.
How to do the upgrade:
======================
o buy 16 ram chips 411000 (1Mx1 dynamic rams). The speed is
really important. 100ns should be enough but don't play with
races. I took 80ns for mines.
o buy 16 I.C supports for the rams.
o buy 16 small capacitors of 220nF each. Try to get the same
space between pins as on the board, it'll be easiest to
solder them. Do NOT omit/forget theses capacitors.
o buy/get 3 resistors of 33 ohms. Theses resistors are used to
connect the CAS, RAS and RW line of rams to the output driver
LS373. Basically, dynamic rams have null input current (less
than 10 uA), so that you could get another resistor value.
However, theses resistors are needed for waveform
considerations (I beleive).
o now begins the most difficult task. Get a (un)solder pump or
something like that and unsolder the holes where the rams go.
You must be careful. If you have no experience on such
operation, do not do that. In fact it's quite easy (I have a
some experience of unsoldering double sided board), it's quite
easy because holes are empty. That is, there is no component
attached to them, yet.
Start unsoldering the lower board (no component on that side)
and then the upper board. Holes must be empty.
If a hole still remains full of solder (or solder in the
middle), fill it with new solder and then retry. The board is
quite robust, but do not do that do many times.
o Still there? Now sold the 16 supports. DO NOT SOLD MEMORIES.
First because you may damage them. Second because you cannot
unsold components (you'll damage the board and connections).
SOLD SUPPORTS.
o sold capacitors and resistors.
o Now, do not plug memories on their support. Check that your
computer is still alive.
o Plug one chip, and test your computer. The atari will not
recognize it but this is a test.
o Plug 15 other rams and check your computer.
If everything goes well, the atari recognizes the new memory
bank.
Power supply:
=============
No problem if you upgrade a MegaST2. The MegaST4 has the same
power supply unit as MegaST2.
Testing memory:
===============
Testing memory is a very simple task. Here is a simple exemple
on how to test memory. Basically, the program checks that all bits of a
byte can get the value 0 and 1.
register char *p
register char c;
p = 0x0800; /* First address in not-protected space */
while (1){
c = *p; /* Get a byte */
*p= ~c; /* Toggle each bit and read it again */
if ( *p != ~c ){
printf( "Problem at %08xl [%02x]\n" , p , *p ^ (~c) );
break;
}
*p = c;
if ( *p != c ){
printf( "Can't set old value at %08xl\n" , p );
break;
}
p++;
}
Oops!! I forget to say that you cannot test the memory where
your program is (known as self code modification).
Well, if you can't write a test program, don't worry, and
remember that the Atari uses the last 32K bytes of memory for the
screen. (if the desktop appears on the screen, you are safe!!)
If you have a st520 and you want to add memory, just to the same
things but replace 411000 by 41256. You cannot put 1Mb memories.
Good luck!!
- - - - - - - - - -
The probability of someone watching you is proportional
to the stupidity of your action. - A. Kindsvater
- - - - - - - - - -
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