If the application is battery powered and you have no mains synch available ,it is possible to use a cmos inverter stage (4069) to drive a clock crystal (32.768 KHz)-> fed into a 15 stage binary counter -> to obtain a 1 second square wave (a 4020 will divide down to 2hz...which you can halve in software). Although all this and more can be found internally to most RTCs.