hey anup tuladhar, hows life dear.

don't get hurt from the people who answered you , they have a habit of playing instead of helping..i don;t know y the administrator of this forum ban those who play around instead of giving the right answer to the user.

any ways..

i may not the best person who can give u any advice but here goes nothing;

what you are trying to design is basically a PABX with DISA and OGM feature.

DISA means Direct Inward System Access:
this feauture enables the user to dial the numbers in order to get the system working on their commands.
i don;t know which chip will perform this function but i will find out for you or you can also do a search


OGM means out going message:
this guides the user to do what ever is needed for this you can use speceh IC like of SP..i don't exactly remember the number of the chip but is sp series.

One basic thing you must understand is that you have develop a small PBX ...now the question arise if you only want to show a proto type project then you can design it for one external lines but if professionla then man its too big for a month.

Now your external telephone no. lines will be connected your circuit for this you have design a TLIC i.e. telephone line interface circuit, which involves optical coupler which can separate your circuit supplies with external telephone line supply , relays etc..

Now the controller will monitor a bit lets say bit P2.0 ( as every one knows my favourite:) bit ) to see if a call is coming here or not this is done by connecting the optical coupler with in between controller and external line.

as soon as the call comes controller activate the OGM chip and DISA chip and wait for the user to press the digits required if the user press correct digits then controller takes the input digit compare it some sort of lookup table and then take data from eeporm or any computer....


this may not be enough for you but still i have tried.
waqar