Dear Erik

Thanks for the response.Now for some elaboration,

1. I'm using the 8255 more due to constraints of availabilty. I understand that Philips has an I2C which is more suited to Microcontrollers.

2. Base address.

Let's say I connect P1 of the AT89c51 to the data pins of the 8255.Next I have to initialise the control register, and also the ports namely A,B and C.

For this I have to move data to the control / ports of the 8255.

Going by what you have mentioned as memory mapping, how do I do the memory mapping?Is it software driven or hardware driven?When I use the equate command namely " thang equ 0ffh", how will the controller know that the address specified is external and not internal?

Secondly can I drive a LCD Module by directly connecting it to the AT89C51?

Trust I have made myself a bit more clear.

Regards
Pramod