US Patent 7702981 Structural testing using boundary scan techniques

A boundary scan technique to generate toggling waveform such as a square wave signal to perform structural testing is disclosed. An instr_extesttoggle command is provided that enables IEEE 1149.1 boundary scan cell to selectively generate the toggling signal on the pre-specified output pads of the integrated circuit. The frequency of the toggling signal may be controlled by the JTAG clock signal and the frequency of the toggling signal may be independent of the length of the boundary scan chain. Such an approach circumvents provisioning test points on the interconnects of a printed circuit board.