Semiconductor device and communication system

A semiconductor device comprising:

• an interface configured to receive, from outside, write data transmitted by serial communication;
• a updating controller having a relative calculator configured to perform calculation based on the write data;
• and
• a register configured to store duty setting data indicating a duty value for pulse-width modulation,
• wherein
• the write data incudes:
• a sign data indicating decrementing or incrementing;
• a gain data indicating a gain value;
• and
• a relative value data indicating a relative change value,
• the relative calculator calculates a calculation result by decrementing or incrementing, according to the sign data, a current value of the duty setting data by a value obtained by multiplying the relative change value by the gain value, and
• the updating controller updates the duty setting data according to the calculation result.