A 2.5MByte RAM Expansion for the Atari ST  by Christopher Hicks
 =========================================  (89cmh@uk.ac.cam.eng)
 This document details the addition of an extra 2MBytes of RAM  to 
 a  standard  520/1040 STF/STFM.  The motherboard  I  upgraded  is 
 marked C070789-001 REV D (1040 STF), but this procedure should be 
 OK  for  other  revisions,  except that the  IC  numbers  may  be 
 The existing RAM consisted of thirty-two 256K by 1 DRAMs, mounted 
 under the power supply.  This procedure replaces sixteen of these 
 with two 1MByte SIPs, giving a total of 2.5MBytes.
 Although  this  procedure  worked  perfectly  for  me,  I  cannot 
 guarantee  that  anyone  else can perform  this  upgrade  without 
 damaging their computer.  I therefore disclaim any  responsibilty 
 for  any  damage that may occur as a result  of  attempting  this 
 upgrade. It will also void any warranty on your computer. 
 On  a more positive note,  there is no reason why someone who  is 
 experienced  in  wielding a soldering iron,  and  has  done  some 
 electronic  construction/troubleshooting,  should not be able  to 
 perform this upgrade successfully.
 The  ST's memory management unit (MMU) can support two  banks  of 
 RAM  (upper  and  lower).  These may each  contain  512KBytes  or 
 2MBytes.  In addition the upper bank may be empty.  This arrange-
 ment gives rise to the following memory configurations:
          Lower Bank     Upper Bank     Total
          ==========     ==========     =====
     1.     512 kB          ---         512 kB
     2.     512 kB         512 kB         1 MB
     3.       2 MB          ---           2 MB
     4.       2 MB         512 kB       2.5 MB
     5.     512 kB           2 MB       2.5 MB
     6.       2 MB           2 MB         4 MB
 This  upgrade  converts a machine from configuration 1  or  2  to 
 configuration 5.  An extra address line is required for the 2  MB 
 bank. This is obtained from the MMU (U56) pin 64. 
 Device Pin Diagrams
  1. 256kbit DRAM
   A8 |1          16| GND
    D |2          15| CAS
   WE |3          14| Q
  RAS |4          13| A6
   A0 |5          12| A3
   A2 |6          11| A4
   A1 |7          10| A5
  Vcc |8           9| A7 
  2. 1MByte SIP
     1     Vcc           11    A4            21    WE
     2     CAS           12    A5            22    GND
     3     DQ0           13    DQ3           23    DQ6
     4     A0            14    A6            24    NC
     5     A1            15    A7            25    DQ7
     6     DQ1           16    DQ4           26    Q8
     7     A2            17    A8            27    RAS
     8     A3            18    A9            28    CAS8
     9     GND           19    NC            29    D8
     10    DQ2           20    DQ5           30    Vcc
  NB Pins 26, 28 and 29 refer to the ninth bit required for        
     IBM PC systems. This bit is not required on the ST upgrade.
               |                              |
               |   Chips mounted this side    |
               |                              |
               1                              30
 Pin Functions
 A0 - A9     Address inputs (row/column multiplexed)
 CAS         Column address strobe
 RAS         Row address strobe
 D           Data input
 Q           Data output
 DQ0 - DQ7   Data combined inputs/outputs
 WE          Write Enable input
 Vcc         Power (+5V)
 GND         Ground (0V)
 NC          Not connected 
 Parts Required
 1.  Two 1M x 8, or 1M x 9 SIPs, 120ns or faster
 2.  Two 16 pin and two 14 pin IC sockets 
 3.  A small piece of veroboard (big enough to mount the two SIPs)
 4.  A few dozen short bits of wire (a shredded scrap of ribbon
     cable is ideal - lots of colours for easy identification!)
 Total cost - about 80 pounds including VAT!
 The motherboard and SIPs may be damaged by static electricity, so 
 don't  work on this project wearing synthetic clothes and  rubber 
 shoes  on  a nylon carpet etc...   Seriously  though,  no  damage 
 should  occur  if  you are reasonably  careful  (use  a  grounded 
 soldering  iron,  and  don't work on a highly waxed  or  polished 
 surface, for example).
 1.   Remove the motherboard from the computer,  and identify  the 
      RAM chips (U 3>6,  10>13,  18>25, 27>30, 34>37, 39>42, 44>47 
      on my 1040STF). On a 520 only half of these will be present, 
      and step 2 may be skipped.
 2.   Desolder  and  remove the upper bank  of  DRAMs.  These  are 
      scrap,  so don't worry about damaging them, but do take care 
      not  to  damage any tracks on the motherboard.  On  my  1040 
      these were the right-hand 16 chips (nearest the FDD), though 
      I  know  that on some boards (marked REV 4 ?) it is  the  16 
      nearest  the rear of the computer.  (The way to tell if  you 
      are unsure is that all the pin 4s of each bank are connected 
      together, but the two banks are separate.)
      When these DRAMs have been removed, the computer should work 
      as  a 520ST.  If it doesn't,  the safest recourse is to  buy 
      thirty-two  16-pin  IC sockets,  and sixteen 256k  x  1  bit 
      DRAMS.  Remove  all  the DRAMS  from  the  motherboard,  and 
      replace them with sockets.  Then fit one of the new DRAMS in 
      each  of  sixteen sockets,  and move them until you  find  a 
      combination that works. You then have a 512k lower bank, and 
      an empty upper bank as required.
 3.   Mount the four IC sockets on the veroboard,  end to end, and 
      butted  up together,  so as to make two 30-pin SIP  sockets. 
      The connections on these will, from now on, be refered to as 
      SIP1 pins 1 thru 30, and SIP2 pins 1 thru 30.
 4.   Break  the  veroboard tracks between the following  pins  on 
      SIPs  1 and 2:  2,3,6,10,13,16,20,23,25,26.  This  operation 
      separates the data and CAS lines on the two SIPs.
 5.   Connect together the following veroboard tracks: 22, 28, 29. 
      This disables bit 8 if present, leaving bits 0>7 for the ST.
 6.   Decide  where the expansion board is to go.  Mine is in  the 
      space  normally occupied by the TV modulator and  associated 
      circuitry. Bear in mind that leads to the board should be no 
      more than about 6 inches long to avoid capacitance problems.
 7.   Back  to the motherboard...  Using a continuity  tester  you 
      should find that the CAS lines (pin 15) of the removed DRAMs 
      are connected together in two groups of eight.  Take a short 
      wire from one of these groups of pin 15s to SIP1 pin 2,  and 
      another from the other group of pin 15s to SIP2 pin 2.
 8.   Take wires from the pin 2s of the first group of eight DRAMs 
      to pins 3, 6, 10, 13, 16, 20, 23, 25 on SIP1.
      Similarly connect the pin 2s of the second group of DRAMs to 
      pins 3, 6, 10, 13, 16, 20, 23, 25 on SIP2.
      The databus is now connected up,  and the complicated bit is 
      over.  Note  that  it is essential that CAS (pin 15)  and  D 
      (pin 2) of each DRAM are taken to the same SIP.
 9.   Now wire A0 > A8, WE, Vcc, GND and RAS from the SIP board to 
      the similarly named pin of any of the vacated DRAM slots.
 10.  Lastly  wire  pin 18 of the SIP board to pin 64 of  the  MMU 
      (U56 on my board).  To aid identification, the part no of my 
      MMU is C025912-38. Pin numbers are marked on the board.
 11.  Make   sure  there  are  no  shorts,   and  check  all   the 
      connections.  Insulate  the  back of the SIP  board  (eg  by 
      taping a piece of card over it) and insert the SIPs.
 12.  Reassemble the computer and hey presto - a 2.5Meg ST.
 13.  Give a copy of this documentation to anyone you please,  for 
      them to try the same upgrade.
 14.  When  you run out of memory again,  repeat exactly the  same 
      procedure,  replacing the other sixteen DRAMS,  and you will 
      find that you have a 4 Meg ST - what could be simpler?
 If  you  make use of this upgrade,  please drop me a line  at  my 
 email address,  and I will send you details of any other hardware 
 hacks I succeed with! Good luck...
P.S. I don't have transatlantic e-mail facility. So, if sent from the other
side of the Atlantic, it is most likely that I shall not be recieving it.
However, if you have any sugestion or criticism, please send to the address 
M.A.Rahin@lut.ac.uk, who will redirect to me.
                                        | The Final Value Theorem:
  Christopher Hicks 89cmh@uk.ac.cam.eng |  The answer you get is
                    cmh21@uk.ac.cam.phx |     always wrong...


(C) Marko, Suomen Atari-sivut / ArkiSTo 2003