| 摘要 |
PROBLEM TO BE SOLVED: To provide a semiconductor device having a programmable impedance control circuit capable of simple impedance updating control. SOLUTION: The programmable impedance control circuit is provided with a clock frequency dividing signal line 61, which is the signal line of a clock frequency dividing signal dividing the frequency of a system clock CK in the same cycle as the updating cycle of the impedance of an output buffer, and a voltage comparator circuit 51 compares a current VZQ flowing in an external resistor RQ with a current DBUF flowing in a dummy buffer by the clock frequency dividing signal 32 CK. Then, an up/down counter circuit 52 controls an output buffer size on the basis of the compared result of the voltage comparator circuit 51 synchronously with the system clock CK and in a specified operating state such as read, write or Nop activating an OE signal, an updating control register circuit 53 updates output buffer size data.
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