Lecture-3
Bussed Architecture
The basic components of a microcomputer, as discussed
earlier, are:
1) CPU
2) Program memory
3) Data memory
4) Output ports
5) Input ports
6) Clock generator.
The clock generator generates the appropriate clock pulses for the
synchronized operation of different components of microcomputer.
The clock generator is on-chip in Intel 8085A microprocessor. Now,
the question comes, how the microprocessor is connected to other
components - memory and I/O ports. One possibility is that all the
memory chips and ports are connected separately to CPU as shown
in fig.1.2.
Program Data Data
Memory Memory Memory
Clock Output
Generator
CPU Device
Input Input Output
Device Device Device
Fig.1.2 Separate Connection of Memory and I/O Devices with CPU
, In this case, large no of address lines, signal lines, input and output
lines are required from the CPU. The size of the CPU increases much
if all the components are to be simultaneously controlled. The
capability of expanding the system by adding more components will
be limited. If a CPU is fabricated on a chip such that it provides
interface to N devices, adding one more device will be impossible.
The system becomes too complex, therefore, bussed architecture is
used to connect component to the microprocessor.
The Bussed Architecture for Microprocessor:
The first question is what is a ‘Bus’? Bus is a group of parallel
lines that connect two or more devices. It carries information in bits.
Whenever processor (CPU) needs to access any memory or I/O
device of the microcomputer system, it does so by setting up signals
on the address bus to identify the appropriate circuit. Data may be
transferred by means of data bus, in required direction between the
device and the processor. Signals on the control bus serve a number
of purposes such as control the transfer of data direction.
2 3 N
1 ....
Fig.1.3 Data Bus Shared by ‘N’ Devices
Bussed Architecture
The basic components of a microcomputer, as discussed
earlier, are:
1) CPU
2) Program memory
3) Data memory
4) Output ports
5) Input ports
6) Clock generator.
The clock generator generates the appropriate clock pulses for the
synchronized operation of different components of microcomputer.
The clock generator is on-chip in Intel 8085A microprocessor. Now,
the question comes, how the microprocessor is connected to other
components - memory and I/O ports. One possibility is that all the
memory chips and ports are connected separately to CPU as shown
in fig.1.2.
Program Data Data
Memory Memory Memory
Clock Output
Generator
CPU Device
Input Input Output
Device Device Device
Fig.1.2 Separate Connection of Memory and I/O Devices with CPU
, In this case, large no of address lines, signal lines, input and output
lines are required from the CPU. The size of the CPU increases much
if all the components are to be simultaneously controlled. The
capability of expanding the system by adding more components will
be limited. If a CPU is fabricated on a chip such that it provides
interface to N devices, adding one more device will be impossible.
The system becomes too complex, therefore, bussed architecture is
used to connect component to the microprocessor.
The Bussed Architecture for Microprocessor:
The first question is what is a ‘Bus’? Bus is a group of parallel
lines that connect two or more devices. It carries information in bits.
Whenever processor (CPU) needs to access any memory or I/O
device of the microcomputer system, it does so by setting up signals
on the address bus to identify the appropriate circuit. Data may be
transferred by means of data bus, in required direction between the
device and the processor. Signals on the control bus serve a number
of purposes such as control the transfer of data direction.
2 3 N
1 ....
Fig.1.3 Data Bus Shared by ‘N’ Devices
