But Motorola family of microprocessors like 6800, 68000, 68020, etc. So some I/O ports can be connected as I/O-mapped I/O ports, and some others as memory-mapped I/O ports in an Intel processor-based system. provide I/O-mapped I/O facility, in addition to providing memory-mapped I/O. The Intel family of microprocessors like 8085, 8086, 80386, Pentium, and Zilog family of microprocessors like Z-80, Z-8000, etc. Both of them have their advantages and disadvantages. And only memory-accessing instructions like MVI, MOV, LOAD, SAVE are used to access the I/O devices.Īfter the discussion stated earlier, it is not possible for us to conclude to which scheme of addressing the Input Output ports is better. This is underutilisation of the resource. If the peripherals are connected in memory mapped fashion, then total devices it can address is only 64K. Here we fully utilize the addressing capacity of the processor. And special instructions IN and OUT are used to access the peripherals. If we connect I/Os to it an I/O-mapped I/O then, it can address 256 I/Os + 64 KB memory. Let's take an example of the 8085 processor. In this case, instructions used to access I/Os are the same as that used for memory. This is underutilisation of resources if your processor supports I/O-mapped I/O. So, total addressed capacity is memory connected only. Memory-mapped I/Os share the memory space with external memory. A separate signal is used for addressing an I/O device. Separate I/O-related instructions are used to access I/Os. So, total addressed capacity is the number of I/Os connected and a memory connected. I/O mapped I/Os have a separate address space from the memory. I/O is any general-purpose port used by processor/controller to handle peripherals connected to it. The ALU operations are not directly applicable to such Input-Output data. Only IN and OUT instructions are accessed by such devices. We give an Input-Output address to an Input-Output device The Input-Output device data are also given to the Arithmetic Logical Unit. We allocate a memory address to an Input-Output device.Īny instructions related to memory can be accessed by this Input-Output device. Before having a discussion regarding the demerits or merits of I/O mapped I/O and memory-mapped I/O, let us have a generic discussion regarding the difference between I/O mapped I/O and memory mapped I/O.
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