
180 THE x86 MICROPROCESSORS
WR
RD
ADDRESS BUS
8086
OUTPUT
PORT
INPUT
PORT
DATA BUS
Figure 5.1 | I/O ports with address bus and data bus and the read and write control signals
5.1.1 | Memory Mapped I/O
In this scheme, the I/O device has the same address space and addressing scheme as memory.
For example, given the instruction MOV AL, [3456H], the address 3456H may be a memory
location or the address of an I/O device. at means, that if there are 50 I/O devices in a system,
the address space available to memory gets reduced by 50. However, that also means that I/O
does not need any special instructions for access, and also that data from/to I/O can ...