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To read or write from a hardware device, special port I/O instructions are used.įrom a software perspective, this is a slight disadvantage because more instructions are required to accomplish the same task.įor instance, if we wanted to test one bit on a memory mapped port, there is a single instruction to test a bit in memory, but for ports we must read the data into a register, then test the bit.
#Memory mapped io Pc
On the older PC compatible machines, only 10 bits of address space were decoded for I/O ports and so there were only 1024 unique port locations modern PC’s decode all 16 address lines. The advantage to this system is that less logic is needed to decode a discrete address and therefore less cost to add hardware devices to a machine. An example of this is the standard PC which uses 16 bits of port address space, but 32 bits of memory address space. The address lines are usually shared between the two address spaces, but less of them are used for accessing ports. Answer (1 of 4): From my perspective as someone who has worked on processor and memory system architecture, memory mapped I/O has more advantages than disadvantages. This is usually accomplished by having a different set of signal lines to indicate a memory access versus a port access. I/O devices are mapped into a separate address space. However, even with address space being no longer a major concern, neither I/O mapping method is universally superior to the other, and there will be cases where using port-mapped I/O is still preferable. Therefore, it has become more frequently practical to take advantage of the benefits of memory-mapped I/O. Intel has, for the most part, used the I/O mapped scheme for their microprocessors and Motorola has used the memory mapped scheme.Īs 16-bit processors have become obsolete and replaced with 32-bit and 64-bit in general use, reserving ranges of memory address space for I/O is less of a problem, as the memory address space of the processor is usually much larger than the required space for all memory and I/O devices in a system. The difference between the two schemes occurs within the Micro processor’s / Micro controller’s. I/O mapped I/O uses a separate, dedicated address space and is accessed via a dedicated set of microprocessor instructions. Memory mapped I/O is mapped into the same address space as program memory and/or user memory, and is accessed in the same way. However, as far as the peripheral is concerned, both methods are really identical. I/O Mapped I/O (also, known as Port Mapped I/O).Of 600,000 men, 12,000 slaves, and 80 camels carrying 300 pounds of gold each.Normally, Micro -Controller’s / Micro -Processor’s use two methods to connect external devices: Ruler of the Mali Empire, arrives in Cairo on his way to Mecca, with a procession
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