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000005 M70. PowerBoard ClockUp

   ***************************** WARNING*************************************** 

                 This is for Mod.70 PowerBoard,  not for 8580.

   *********************************************************************************
      40MHz base clock setting for Mod.70 PowerBoard. 
      Originally written by F355 ( Psudenym in FIBMJ ) on 1999.04.26 
      Translated by Sandy  on 2000.05.10

      Please be advised that F355 and I are both not responsible for any
      damage  or inconvenience on your system with following script. 

 

  1. You need to solder off just * one * of the pins of PLLIC.
     Search PLLIC marked IMI SC-427BYB atop on the chip. It's a tiny SSDP  type chip with 10 pins
     on each side. It locates around pin #1 of big blue translucent chip, just between OSC marked H14318
     and flash ROM socket. 

  2. Heat up pin #9 of PLLIC, solder off the pin from the board.
      the target pin is "pulled- up" internally in the chip and if you float  the pin from the board, electrical
      status of the pin will turn to  *High*. 

  3. Set  J11 jumper to the position for 25MHz operation ( J11= ON ).

  Now the output frequency of the PLLIC is 40MHZ.  Keep in mind, Cyrix 100/120/133  in x4 multiplied speed
  and  DX4-100 may not work.  Only am5x86 x4/x3 will run on the board ( on WinXX ).
  (  Errm.... There *IS* such CPU, Cyrix 5x86 GP120 x4, actually.  ) 

   Pin out of IMI SC-427BYB 
                 _____________
              | o           |
        Xin = |1          20| = 14.1318MHz 
       Xout = |2          19| = VDD
        Vss = |3          18| = PD2
   7.159MHz = |4          17| = VCOin2
         S0 = |5          16| = 16NHz
     VCOin1 = |6          15| = 32MHz 
        PD1 = |7          14| = VSS
        VDD = |8          13| = MCLK2
         S1 = |9          12| = S2
      MCLK1 = |10         11| = TS
              |_____________|

        "o" is orientation marking.

         S1 ( pin #9 ) should be soldered off from the planar.
 

    Combination of Pin Logic and Output Frequency
 
           Input       Out Put   Jumper 
  S2   S1   S0     CPU Base Clock     J11
   0    0    1      25MHz     ON
   1    0    1      33MHz     OFF
         
   0    1    1      40MHz    ON

 ** S1 is internally high and physically grounded( pulled down ) to Vss in original circuit.  So it is always
        *LOW*.   S0 is pulled up to Vcc through R255 on the board, It is always  *HIGH*. 
       Changing base clock  between 25MHz and 33MHz is done by J11.  If the jumper set is ON, S2 will
       be  grounded *LOW* (=0 ), while it is  OFF then  S2 will be *HIgh* ( =1 ).
       To get 40MHz,  set S1 *HIGH* ( this is done by soldering off the pin  #9 from the board ), and set
       S2 *LOW*( J11=ON ).

      Attention to you all
      PLLIC is very little and pins are very close to each other.  Furthermore 14.318 OSC locates very 
      close to PLLIC.
      Be careful not to break off the pin, nor to make a bridge between pins by your soldering iron. 
      Otherwise your system will not work on 25/33MHz  anymore.  It may  cause fatal errors on your
      expensive PowerBoard.
 

      DO IT WITH YOUR OWN RISK !  NO ONE WILL BE RESPONSIBLE BUT YOU.
      and
      TAKE CARE ! 

     If anybody wants to amend above method to *CORRECT*  English, please do it.
     If you can connect lead wires to floated pin #9 and it's solder land each,  and set jumper pins on the
     other end, you can change back to normal  setting with shorting the jumper pins.

     About Mod.80 Powerboard.
     PLLIC used in Mod.80 board is IC DESIGNS 2028SC-B. I  have no pin-out  for it. 
 
 

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