Circuit and method for adjusting pull-up voltage of bus according to pull-up voltage of slave unit

The invention discloses a circuit and method for adjusting the pull-up voltage of a bus according to the pull-up voltage of a slave unit. The circuit comprises the bus, a voltage dividing unit, a comparator, a latch and an impedance unit. Voltage output by a first power source is divided through the voltage dividing unit so that divided voltage can be obtained; the first input end of the comparator receives the divided voltage, the second input end of the comparator receives the pull-up voltage of the slave unit through the bus, and the output end of the comparator outputs a comparative result; the first input end of the latch receives the comparative result, the second input end of the latch receives a trigger signal, the output end of the latch outputs a control signal to control the resistance value of a pull-up resistor of the bus to have access to the impedance unit, the pull-up voltage formed by the pull-up resistor of the bus is equal to the pull-up voltage of the slave unit, and voltage matching is achieved. By means of the mode, the pull-up voltage on the bus can be increased automatically according to the working voltage of the slave unit, and then the voltage matching is achieved.