Transcript Deployment of Sensing Devices on Critical Infrastructure

Microprocessor
Dr. Rabie A. Ramadan
Al-Azhar University
Lecture 6
Interfacing I/O Devices
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I/O modes

Serial Mode


Data entered or exited in serial
Parallel Mode
• Data entered or exited in parallel
• Interfaced through:
• Peripheral mapped I/O
• Each device has a 8-bit address and enabled by I/O
related control signals
• Memory mapped I/O
• Each device has a 16-bit address and enabled by
memory related control signals
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Interfacing I/O Devices

The Z80 uses the instructions:
•
• IN to read (input) data from an input device and
• OUT to write (send) data to an output device.
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OUT Instruction

It can send data from the accumulator, internal-purpose
registers, or memory registers to an output device.

The OUT instructions include:
• 8 bit address of a device as an operand.
• The address range from 00H to FFH is called the I/O or
peripheral map,
• An address can be referred to as a device address, port
address, or port number.
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Example

When the microprocessor reads and executes the machine codes written at
memory register 2050H and 2051H, it will transfer (copy) the byte from the
accumulator to the LED port with address 07H and display the byte.
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Execution of OUT Instruction
and Timing

The OUT has three machine cycles;

The Z80 reads the opcode and the port address
from memory in the first two machine cycles and
writes into the port in the third cycle.
• Opcode Fetch,
• Memory Read and
• I/O Write.
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Execution of OUT Instruction
and Timing
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Execution of OUT Instruction
and Timing
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Basic Concepts in Interfacing
Output Devices
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Basic Concepts in Interfacing
Output Devices
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Illustrative Example 1:
Interfacing LEDs



Hardware
7475 Latch
• 4 D-Latches
• 2 enable lines
47LS373 Octal Latch
• Latch followed by
tri- state buffer
• Reduces using
the data bus
• 8 latches instead of 4
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Interface Circuit
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Interface Circuit
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Using a Seven-Segment LED as
a Display Device
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Using a Seven-Segment LED as
a Display Device
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Interfacing INPUT Devices

IN instruction
• Read (copy) data from such input devices as switches,
keyboard, and A/D data converters.
• Can read an input device and place the data into the
accumulator, Z80 registers, or memory registers.
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Example

First read the machine codes stored at locations 2065H and 2066H,

Read the switch positions at port 84H by enabling the interfacing
device of the port.

The data byte indicating switch positions from the input port will be
placed in the accumulator.
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Execution of IN Instruction and
Its Timing

The IN instruction has three machine cycles:
• Opcode Fetch,
• Memory Read  port address
• I/O Read.
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Execution of IN Instruction and
Its Timing
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Illustrative Example :
Interfacing Input Switches
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Multiple Port Addresses

the address lines A4 and
A3 are not used by the
decoding circuit; the logic
levels on these lines can
be either 0 or 1.
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
Some other examples from the book
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