When a host computer determines that a firmware version to be loaded is higher than a firmware version of each chip to be loaded, the host computer sends a loading flag to the chips to be loaded to enable the chips to be loaded enters a loading mode. The host computer redefines multiple controllable physical connections between each chip to be loaded entering the loading mode and a master controller chip connected thereto so that they act as loading buses. Each chip to be loaded executes a loading process according to a frame period and a frame count to receive the load file completely and then executes the IAP command to program its ROM. When each chip to be loaded finishes the loading process, each chip to be loaded jumps out of the load mode, and the host computer restores the definitions of the plurality of controllable physical connections.