An output interface circuit comprises a terminal connected with an external equipment, a
source level converting circuit connected with the terminal, a drain level converting circuit connected with the terminal, a
dip switch and a control device; when the operator operates the
dip switch to select the source output corresponding mode, the
source level converting circuit converts the level of an output
signal of the control device to a high level and outputs to the external equipment; when the operator operates the
dip switch to select the drain output corresponding mode, the drain level converting circuit converts the level of the output
signal of the control device to a high level and outputs to the external equipment; an input interface circuit comprises a terminal connected with the external equipment, the dip switch, the drain level converting circuit connected with the terminal, the
source level converting circuit connected with the terminal, and the control device; when the operator operates the dip switch to select the drain input corresponding mode, the drain level converting circuit converts the level of an input
signal of the terminal to a low level and inputs to the control device; when the operator operates the dip switch to select the source input corresponding mode, the source level converting circuit converts the level of the input signal of the terminal to a low level and inputs to the control device.