Device such as expansion card, access control method of the expansion card, and a memory medium storing a program capable of being read by computer

A control method for use with an expansion device connected to an expansion bus, having a clock generator for generating a reference clock, comprising:

• a receiving step, of receiving a data transmission clock supplied through the expansion bus;
• a generating step, of generating a reference clock by means of the clock generator;
• a first dividing step, of dividing the reference clock with a first frequency division ratio;
• a control step, of controlling the clock generator so that a divided clock divided in said first dividing step synchronizes with the data transmission clock;
• a second dividing step, of generating an operation clock of the expansion device by dividing the reference clock with a first frequency division ratio;
• and
• a setting step, of setting arbitrary numbers as the first and second frequency division ratios.

An expansion device connected to an expansion bus, comprising:

• a clock receiver, that receives a data transmission clock supplied through the expansion bus;
• a clock generator whose output is a reference clock;
• a first frequency divider, arranged to receive the reference clock, and outputting a first frequency-divided signal obtained by dividing the reference clock with a first frequency division ratio;
• a controller that controls said clock generator so that an output of said first frequency divider synchronizes with the data transmission clock;
• a second frequency divider, arranged to receive the reference clock, and outputting an operation clock of the expansion device by dividing the reference clock with a second frequency division ratio;
• and
• a setting means for setting arbitrary numbers as the first and second frequency division ratios to said first and second frequency dividers, respectively.