Hi Aijaz,

you wrote:
i've read the 8051 by m mazizdi. in the pins on the pins he says to configure any port as a input port we should write 1's to all its pins. but i have a device mitel's 88435 connected to it. won't it have any efect on it's(88435's) operation? also is the confiuration done once and for all or is it done before interfacing?
please do help me out 'cuz my prject has been stalled.

You only need to write a 1 to the port pin you want to function as a input. This can be done with the SETB <bit> (set bit instruction).

When you use the byte write instructions (ie. mov P0, A) it will affect the port pins you want to use as output pins. So you do need to be careful on how you set these port pins.

If you are writing your program in assembly and have tons of program space then just keep it simple and use the bit oriented instructions.

When you use the byte write instruction this will have an effect upon the other pins which you might not want.

Regards,

Charles Bannister