Help required with 22V10 - Using a pin as Input an Output

[Dave Hitchins]

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.

[Phil Allison]

Dave Hitchins wrote:
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Hi Dave,

WTF makes you think your is a *basic* question about * electronics * ??????????????

You DID even read the NG name ??
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