4-9
SYSTEM REGISTER ORGANIZATION
4.6 ADDRESSING MODES
Combinations of the value of ESE bit and the individual remap bits in the REM APC FG regi ster
yield four different peripheral addressing modes for I/O address decoding.
4.6.1 DOS-compatible Mod e
DOS-compatible mode is achieved by clearing ESE and all the peripheral remap bits . In this
mode, all PC/AT-compatible peripherals are mapped into the DOS I/O space. Only address lines
A9:0 are decoded for internal peripherals. Accesses to PC/AT-compatible peripherals are valid,
while all other internal peripherals are inaccessible (see Figure 4-5).
This mode is useful for accessing the internal timer, interrupt controller, serial I/O ports, or DMA
controller in a DOS-compatible environment.