| 摘要 |
A computer system having a control system for controlling a VGA module built in the motherboard is disclosed. The operation of the internal video module is dependent on the existence of an add-on video card mounted in an expansion slot of the computer system. The control system for enabling and disabling the internal video adapter module includes an IDSEL (device identification signal line) signal masking and unmasking circuit provided at the IDSEL signal line placed between the internal video adapter module and a system bus, wherein the masking and unmasking of the IDSEL signal are responsive to a control signal fed from the computer system; and a system BIOS outputting the control signal supplied with the IDSEL signal masking and unmasking circuit through a general purpose input/output module, wherein the output of the control signal is dependent on the existence of an add-on video card mounted in an expansion slot. Initially, the IDSEL signal is set to the unmasked or active state, thereby notifying the computer system of the presence of the internal video adapter module. If the add-on video card is detected, a logic low or OFF signal Sc is outputted to the general purpose input/output module to mask the IDSEL signal applied with the internal video module. With this, the internal video adapter module is automatically disabled. Then the system BIOS performs the initialization routine of the add-on video card.
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