Question: "I replaced the motherboard and/or CPU in my system,
     but the case still shows '33' on the number LED display.  How do
     I change it to '66' (or any other number)?"

     Question: "I replaced my motherboard, but now my case shows '33'
     when turbo is off and '12' when I turn turbo on.  How come it's
     backwards?"


             SETTING SPEED LED DISPLAYS IN CLONE SYSTEMS
             -------------------------------------------

     Many clone systems include a two- or three-digit LED number
     display to indicate the clock speed of the motherboard.  If there
     are 3 digits, the hundreds-digit is usually only a "half-digit"
     capable of displaying only '1' or nothing.

     It is important to first understand that the motherboard does not
     send any speed numbers to the LED display, it only sends a TURBO
     ON/OFF signal.  This is a single line that is set to either a
     HIGH or LOW state by the motherboard to signify turbo or
     non-turbo mode.  On some motherboards, a HIGH signal may mean
     it's in turbo mode, but other motherboards may use HIGH to mean
     non-turbo.

     On the number LEDs, you simply set the LED to create the numbers
     you wish to see.  If your display uses two digits, each number
     LED is made of seven independent segments.

         The 7 segments                   The segments are
         are configured in                typically labeled
         this arrangement:                in this sequence:

              ---                                 A
             |   |                            F       B
              ---                                 G
             |   |                            E       C
              ---                                 D


     To display any given number, you simply pick and choose which
     segments to light up.  The jumper board may have a double-row of
     pins for the ten's-digit LED and another double-row for the
     one's-digit.  The pins may be labeled something like:

           1 G 2 3 1 E 2 3 1 C 2 3 1 A 2
             3 2 F 1 3 2 D 1 3 2 B 1 3

     You'll note letters in there corresponding to each segment of
     that particular LED.  Each letter is surrounded by a 1, 2, and 3
     in a triangular pattern, although to save space the triangles may
     alternately point up and down for adjacent letters.  For each
     letter, you have four choices for jumper placement: connecting
     the letter to 1, to 2, to 3, or no jumper at all.  Jumper the
     letter to 1 if you want that segment to light only in standard
     mode.  Jumper to 2 if you want it to light only in turbo mode. 
     Jumper to 3 if it's supposed to be lit in either mode.  No jumper
     means that segment is not lit in either mode.  (Note you never
     jumper a number to a number.) 

     Depending on whether the LED board expects the turbo signal to be
     HIGH or LOW in turbo mode, the meaning of the 1 and 2 jumpers may
     be reversed.  Remember that some motherboards may reverse the
     meaning of the HIGH/LOW signal on the turbo line.  You don't need
     to know which way your motherboard works - if the converse
     numbers display when you toggle the turbo switch, then simply
     reverse the meaning of the 1 and 2 jumper pins in the above
     explanation.

     If your display includes the hundreds half-digit, the two
     segments used to form the '1' may be wired together and
     controlled by a single triangle of jumpers.  This triangle will
     often be added as an 'H' segment to the end of the double-row of
     jumper pins for one of the other two numbers.

     The turbo light is often connected to the number display board
     with a simple two-wire connector.  Your display board may have
     three pins for this connection.  Place the turbo-light connector
     on the left and center pins to light up when the motherboard's
     turbo signal is HIGH, or on the right and center pins to light up
     when the turbo signal is LOW (or vice-versa).  You want the light
     to turn on only when in turbo mode, but the display board doesn't
     know whether your motherboard uses the HIGH or LOW signal to mean
     turbo-ON, hence the three pins give you both options.  Note: the
     turbo light is a polarized LED, so if it doesn't light in either
     mode, you may have the connector reversed.  Try rotating it 180
     degrees and reconnecting it.

     In addition to the turbo signal line and turbo light connector,
     your display board should also have power and ground connections.

     Since you can independently control each segment of the display,
     you don't even have to limit your display to numbers.  You can
     get creative and display 'HI' and 'Lo' instead of '66' and '33'. 
     Or 'UP', 'dn', 'hi', 'On', or ...?  Or set your 386SX20 to
     display '90' and watch your friends drool over your super system!

     This is by no means the only scheme used in LED display boards,
     but is a scheme commonly used.  With this understanding of how
     the typical display works, you may be able to figure out if your
     display board is a variation of this.



     Feb 1, 1994
     
     Dan Goodell
     71520,3116