i,ve built a adc circuit using ADC0804 chip and interfaced it to pc,s parellel port.
the LPT1 contains 3 ports ( 0x378 bi directional, 379 input and 37a output). if 0x37a 5th bit is made high (value 32) then 378 port will becone input port. then using the other pins of ox37a adc,s start, read and chipselect can be controlled. one of the pins of ox379 can be used to monitor the EOC signal from ADC. once eoc read signal can be applied and data can be latched from 0x378 port.
ive built this circuit and it worked well. some of the pins of 37a are inverted internally inside pc the same has to be tested properly.
you can set any pin (ie 0 th or 1th or 2 power nth) bit by reading the current value and altering the bit and writing it back to the port.
if you are using any c compiler use inportb(0x37X) for reading and outportb(0x37x, value)
in case you use winapi then use _inp() and _out() functions
hope this information is useful
reply if you have any queries.