The 8086/8088 processor can address up to 64K byte I/O registers or 32K word registers. The I/O address appears on the address lines A0 to A15 for one clock cycle (T1). It may then be latched using the ALE signal. The upper address lines (A16 - A19) are at logic 0 level during the I/O operations.
The 16-bitregister DX is used as 16-bit I/O address pointer, with full capability to address up to 64K devices. In memory mapped I/O interfacing, the I/O device addresses are treated as memory locations in page 0, i.e. segment address 0000H.Even addressed bytes are transferred on D7-Do and odd addressed bytes are transferred on D8-D15 lines.
The 16-bitregister DX is used as 16-bit I/O address pointer, with full capability to address up to 64K devices. In memory mapped I/O interfacing, the I/O device addresses are treated as memory locations in page 0, i.e. segment address 0000H.Even addressed bytes are transferred on D7-Do and odd addressed bytes are transferred on D8-D15 lines.
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