A method of sending information between first and second modules connected by a signal bus comprises generating a clock signal in the first module, and imposing the clock signal on a first line of the bus. A first pattern of bit values is transmitted from the second module to the first module on a second line of the bus, during first half-periods of each period of said clock signal. A second pattern of bit values is transmitted from the first module to the second module on the second line of the bus, during second half-periods of each period of said clock signal, wherein the second half-periods of each period of said clock signal are different from the first half-periods of each period of said clock signal. Information can then be transmitted from the first module to the second module by altering the second pattern of bit values; and information can be transmitted from the second module to the first module by altering the first pattern of bit values.