From: Dejh@daveejhitchins.plus.com   
      
   I'm having problems with the SDA part of an IIC implementation in a AMD 22V10C   
   (not from China!). I can Output data, to the SDA output, but I'm not able to   
   read the SDA input! My CUPL equations, as a whole, compile OK using WINCUPL   
   and the .JED file    
   programs OK.   
      
   These are the intermediate declarations:   
   FCD7  = !nPFC & A7 & A6 & !A5 & A4 & !A3 &  A2 &  A1 &  A0;   
   SCLH  =  FCD7 & !BnWR &  D6 ;    
   SCLL   =  FCD7 & !BnWR & !D6 ;    
   SDAH  =  FCD7 & !BnWR &  D7 ;   
   SDAL   =  FCD7 & !BnWR & !D7 ;    
      
   These are the outputs associated with SDA I/O:   
   PIN 15  =  D7          /* Data line 7 */   
   PIN 18  =  SDAOE   /* SDA output control latch */   
   PIN 19  =  SDA        /* SDA I/O pin */   
      
   This is the equation for the SDA output control latch and sets the SDA output   
   Low when needed. This sections works just fine.   
   SDAOE  =  SDAH    /* Set high - write FCD7 with D7=H */   
                 # !SDAH & !SDAL & SDAOE     /* Set low - write   
   FCD7 with D7=0 */   
                 # !nRST ;    /* Set high - on reset */   
      
   This is the SDA output pin. Pulled high, externally, with a 4K7 resistor.   
   Works as an output just fine.   
   SDA.OE  = !SDAOE ;    /* Only on when 'LOW' output required */   
   SDA        =  SDAOE ;    /* Always low when output enabled */   
      
   This is the problem pin.   
   D7        =  SDA ;    /* SDA input transferred to D7 output on read of   
   FCD7 */   
   D7.OE  =  FCD7 & BnWR ;   
      
   If I toggle the SDAOE latch I can read its state through D7 e.g. I can read   
   SDA output, however, if I set the SDAOE latch High, ready for  read of the SDA   
   INPUT, I can't then read the input - I just read a High value on D7. It seems   
   that the path from    
   the SDA pin through to the & array isn't there!   
      
   Anybody have any clues to what's going wrong? Thanks . . . Dave H.   
      
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