Abstract: A data buffer (23) is positionable between processing devices, such as microcontroller (21) and a digital signal processor (22). Messages are transmitted between the devices via a dual port RAM buffer (31). The amount of storage allocated for transfers in each direction is adjustable via a size register (42) so that, at any particular time, the optimum amount of storage is provided for a transfer in a particular direction. The buffer is particular suited to applications in mobile telephones.

Abstract: A real time clock is arranged to generate output signals indicative of time of day. An oscillating device (101) produces a first clocking signal which is adjusted in response to a calibration value to produce an output clocking signal. A processor (102) re-calculates the calibration value in response to external clocking signals received from a cellular base station for mobile telephones. The clock may be provided within a mobile telephone and the oscillating device may also be used to provide sleep clock signals allowing a high frequency system clock to be de-activated for periods while the telephone is in a stand-by condition.