In this paper, a scanconverter which displays the biological signals of low frequency on CRT for the purpose of easy read-out is attempted to design for using the CRTC, and it stows some good effectivenesses The results obtained in this experiment are as follows : (1) Using only one chip, CRT controller, it can display both waveforms and characters simultaneously. (2) The flexibility of CPU program can be obtained using the sub-microproce ssor function of CRTC chip. (3) The trend of digital data is possible through the graphic function (4) The vibration of displayed waveform can be prevented using the chip simplification and the trigger signal of one chip. (5) Operation with microprocessor malies the expansion and interface easy.