Interfacing in Microprocessor
Interface is the path for communication between two components.
Interfacing is of two types, memory interfacing and I/O interfacing.
Memory
and I/O Interfacing
Several memory chips and I/O devices are connected to a
microprocessor.
The following figure shows a schematic diagram to
interface memory chips and I/O devices to a microprocessor.
Memory Interfacing
When we are executing any instruction, the address of
memory location or an I/O device is sent out by the microprocessor. The
corresponding memory chip or I/O device is selected by a decoding circuit.
Memory requires some signals to read from and write to
registers and microprocessor transmits some signals for reading or writing
data.
The interfacing process includes matching the memory
requirements with the microprocessor signals. Therefore, the interfacing
circuit should be designed in such a way that it matches the memory signal
requirements with the microprocessor's signals.
I/O interfacing
As we know, keyboard and displays are used as
communication channel with outside world. Therefore, it is necessary that we
interface keyboard and displays with the microprocessor. This is called I/O
interfacing. For this type of interfacing, we use latches and buffers for
interfacing the keyboards and displays with the microprocessor.
But the main drawback of this interfacing is that the
microprocessor can perform only one function.
8085
Interfacing Pins
Following is the list of 8085 pins used for interfacing with other
devices −
- A15 -
A8 (Higher Address Bus)
- AD7 -
AD0(Lower Address/Data Bus)
- ALE
- RD
- WR
- READY
Ways of Communication − Microprocessor with the
Outside World?
There are two ways of communication in which the microprocessor can
connect with the outside world.
- Serial
Communication Interface
- Parallel
Communication interface
Serial Communication Interface − In this type
of communication, the interface gets a single byte of data from the
microprocessor and sends it bit by bit to the other system serially and
vice-a-versa.
Parallel Communication Interface − In this type
of communication, the interface gets a byte of data from the microprocessor and
sends it bit by bit to the other systems in simultaneous (or) parallel fashion
and vice-a-versa.
As we
know that any system which process digital data needs the facility
for storing the data. Interfacing is a technique to be used for
connecting the Microprocessor to Memory.
Buffers and Latches have totally
different concepts and usages. They can’t be differentiated, as Buffers can be
considered as a super set of a latch.
Latch is basically a
digital circuit with feedback to hold data onto it. A latch is controlled by an
enable and the input data. When a latch is enabled it follows the input and
throws it at the output, but when disabled the previous value before the enable
going low is latched on to it (Assuming an active high logic). The use of a
latch is just to hold memory and that’s all.
A Buffer on the other hand is
a mixed signal component. Its function
is not just to hold memory but also to increase the drive strength, make the
system noise resistant and so on.
A
latch is like a water tap. When tap
is disabled the water is held on to it, but when enabled it just flows the
water out from the tank without any processing. But a buffer is like a water purifier which does additional featuring to
the water and also has a tap fixed in it.
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