Creating a form of communication with analog i/o?

I want to use a attiny85 as a controller for a 7 segment display, along with a shift register. Can I use an analog pin on an arduino to send a value to the attiny85, and depending on the value it lights up a certain display?

How many 7 segment displays are you talking about?
I assume the shift register is to drive the displays?
How will the arduino be talking to the tiny85?

you could also use a bcd decoder from the attiny85 and simplify the programming, just write the binary to the port
and you would need timers to decode the pwm signal into an actual value, aalso there would be a limit of 255 possible values, not including errors in timing
you may be better off with a one way serial comm, pick a baud rate for your application and use software serial on the attiny