I'm using a P87C591 which has a multi-functional port1.
Port 1 can be used as ADC or digital I/O.From reading the datasheet I gather on reset that pins p.0 and p.1 are driven high and p1.1 through p1.7 are high impedance.
I am trying to use the port for digital I/O to drive a LCD display (no groans please).LCD did not initialize with code and hardware I have used on a P89c51RD2 successfully.
Inspection using CRO shows data on pins p1.0 and p1.1 working correctly but p1.2 through p1.7 are always high.There are pull up resistors on the LCD.
Disconnecting the LCD and using 3k3 pull up resistor is the same result-I cannot drive these lines low.With nothing connected to port1 these pins appear to be floating around 0.3 volts.
Can this port not be used in this manner or should I have initialized one of the registers differently to establish the port for digital I/O ?
Would appreciate a prod in the right direction if possible.