Thursday, 13 June 2013

Isolated I/O and memory mapped I/O

The  isolated I/O  and memory mapped I/O can be differentiated according to device address, control signals, instruction available. The differences are tabulated below:
Properties Memory-mapped I/O Isolated I/O
Device register 16 bit 8 bit
Control signals MEMR/MEMW IOR/ IOW
Instructions available Memory related instruction such as STA, LDA, LDAX, STAX IN/OUT
Data transfer Between any register and I/O Only between I/O and accumulator
Maximum number of I/O possible The memory map (64k) is shared between I/O and system memory I/O map is independent of the memory map; 256 i/p devices and 256 o/p devices can be connected
Execution speed 13 T-states (STA, LDA)7 T–states (MOV M , R) 10 T- states
Hardwire requirements More hardware is needed to decode 16 bit address Less hardware is needed to decode 8 bit address
Other features Arithmetic or logical operations can be directly performec with i/o data Not available

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