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Chapter6

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There are two methods for interfacing memory and I/O devices with a microprocessor: I/O mapped I/O and memory mapped I/O. I/O mapped I/O treats I/O devices and memory separately, while memory mapped I/O treats I/O devices as memory. I/O mapped I/O can use either 8 or 16 address lines, allowing connection of up to 256 fixed I/O devices or 65,536 variable I/O devices. Specific instructions like IN, OUT, and MOV are used to access I/O ports depending on whether it is fixed or variable addressing.

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System Interfacing
Methods of Interfacing • There are two methods of interfacing memory or I/O devices with microprocessor 1. I/O mapped I/O 2. Memory mapped I/O • In I/O mapped I/O, I/O device is treated as a I/O device and memory as memory. • In memory mapped I/O, I/O devices are also treated as memory.
I/O mapped I/O • I/O device is treated as I/O device & memory as memory • Each I/O device uses – either 8 address lines (Fixed port) – or 16 address lines ( Variable port) • In fixed port 256 input and 256 output devices can be connected • Invariable port, 65,536 input & 65,536 output devices can be used
Instructions used in Fixed type addressing • Any address line A0 - A7 or A8 – A15 can be used. • A16 - A19 are all 0’s. • IN AL, 8 bit port address • IN AX, 8 bit port address • OUT 8 bit port address, AL • OUT 8 bit port address, AX
Instructions used in Variable type addressing • Address lines A0 - A15 are be used. • A16 - A19 are all 0’s. • MOV DX, 16bit port address • IN AL,DX • IN AX,DX • OUT DX,AL • OUT DX,AX
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Chapter6

  • 2. Methods of Interfacing • There are two methods of interfacing memory or I/O devices with microprocessor 1. I/O mapped I/O 2. Memory mapped I/O • In I/O mapped I/O, I/O device is treated as a I/O device and memory as memory. • In memory mapped I/O, I/O devices are also treated as memory.
  • 3. I/O mapped I/O • I/O device is treated as I/O device & memory as memory • Each I/O device uses – either 8 address lines (Fixed port) – or 16 address lines ( Variable port) • In fixed port 256 input and 256 output devices can be connected • Invariable port, 65,536 input & 65,536 output devices can be used
  • 4. Instructions used in Fixed type addressing • Any address line A0 - A7 or A8 – A15 can be used. • A16 - A19 are all 0’s. • IN AL, 8 bit port address • IN AX, 8 bit port address • OUT 8 bit port address, AL • OUT 8 bit port address, AX
  • 5. Instructions used in Variable type addressing • Address lines A0 - A15 are be used. • A16 - A19 are all 0’s. • MOV DX, 16bit port address • IN AL,DX • IN AX,DX • OUT DX,AL • OUT DX,AX