Posted on May 17, 2011 at 11:52We would like to use the MCUAD[0..7] as an input port as we are short of port pins. We tried to read the port by making the PA7 as a active high external chip select in the range 0x8100-0x810f controlled with !rd,!wr and or !ale signals. And mapping the adress range to a different bank than the fs[0..7] or csboot[0..3]. When we make the port pin high by directly connecting the pin to VCC, only that particulat port bit is becoming high and all other bits are becoming low( e.g. if MCUAD4 is made high we are reading 0x10). When we tried to pull up the port pin using a 33Ohm resistor also we are getting 0x10, but when we tried to pull it down by either connecting to ground directly or thru a 33Ohm resistor, we are able to read the port but the PC is changing and the program execution is going out of control. Please suggest if we can use this Data bus as GPIO., :-[
