Rauf,

You might do better using Microchip PIC processors for that application unless you have a project time constraint. I have a demo PIC timer that runs a PIC16C54RC/P off a RC oscillator. Its low power, small pinout and keeps reasonable time at office temperatures. I don't mess with PICs myself, so I can't tell you much more than that.

Motorola also makes good solutions for low power applications. They do a lot of specialty versions for large market applicatins. You may find some specialty micro with some good web browsing.

The 8051 running in IDLE mode consumes half the power of normal 8051; much worst consumption than POWER-DOWN mode. This would usually be the reason NOT to use an 8051 for this application. I'd recommend looking at Dallas Semi as they understand both 8051 derivatives and RTCs.

Usually remote control micros are powered OFF until any button is pressed. A power-down state is fine too if you require non-volatile memory values.

External RTCs are designed for low-power applications but the require a small battery of their own. My DS1307 circuit will run 10 years on a 3V 35maH lithium battery.

The RTC usually run off of inexpensive color burst crystals (32.768Khz). The coin sized battery is the only size constraint (remember to add the diode). I usually estimate the cost of a RTC feature as being $4 to $5 in component costs. I'd recommend avoiding external RTC as long as you can unless you need accuracy or calendar scheduling of remote commands.

Hitachi may have a specialty micro for remote controls... you better check them because they may have it all in one package AND an example circuit.

-Jay C. Box