Solution:

The ISA bus timing control function is disabled in the BIOS of PCA-6148, so user cannot change it ib BIOS now. However, user still can change it through direct I/O operation (on VIA VT82C486G). The way to change ISA bus speed is to change RX11H by I/O port A8H and A9H. The register is controlled by I/O address A8H & A9H. A8H works as index to specific which register is to communicate with and A9H is the data register for the specific register. Following is the procedure to change ISA bus speed of PCA-6148. 1. OUTPORTB( A8H,11H) ; it means we want to talk with register RX11H 2. X=INPORTB( A9H) ; get the current setting of RX11H 3. X=X & 87H ; set bit 3 of RX11H to "0" 4. OUTPORTB(A8H,11H) 5. OUTPORTB(A9H,X) ; write new setting to RX11H 6. OUTPORTB(A8H,11H) 7. X=(X->3) * 8 + 5 : change bit 0 ~ bit 2 to "101" 8. OUTPORTB(A9H,X) ; change the setting of RX11H to new setting 9. OUTPORTB(A8H,11H) 10. X=X | 08H ; set bit 3 to "1" 11. OUTPORTB(A9H,X) ; disable ISA bus clock switching The code listed above is pseudocode for reference only.