17.3 Counter/Timer Access and Programming

The emulated 8254 counter/timer chip is accessed through page 0 at addresses Base + 12 through BaseAddress 0 on the chip is equivalent to address 12 in the register map, etc. Before performing any access to the chip, you must set the current page to page 0 with the miscellaneous control register at Base + 8 to ensure that the proper page is enabled. See page 21 for the format of this register. Note that writing page bits to the miscellaneous control register will not implement a board reset or interrupt reset operation as long as the two reset bits are left at 0. Also, writing a 1 to either reset bit in this register will not change the contents of the page bits.

The current page may be determined by reading the page bits at Base + 7 (see page 20).

Once you write the proper page value, you can read and write to the 82C54 registers.