Question

In the computer system, the bus is said to be a collection of wires through which data
is transmitted. The bus could be unidirectional or bidirectional depending on what is
being done at a time. With referenced to the type of buses explain this phenomena or
principle.

Answer 1

Buses A bus is a high-speed internal connection. Buses are used to send control signals and data between the processor and other components. Three types of bus are used. Address bus - carries memory addresses from the processor to other components such as primary storage and input/output devices. The address bus is unidirectional. Data bus - carries the data between the processor and other components. The data bus is bidirectional. Control bus - carries control signals from the processor to other components. The control bus also carries the clock's pulses. The control bus is unidirectional. 02:15 ✓

Reason why bus is unidirectional and bidirectional as explain below with explanation of buses types in above image-

An address bus is a group of lines/wires (16 lines in case of 8085 microprocessor) which "fetch" an address or locate an address in a memory device or peripheral device interfaced with the microprocessor. What is addressing/memory addressing and why it is needed? Simply because, in order to locate a specific data we need to know its location which is nothing but the "address".

|--------------| |--------------------|
| microp. |-----------Address ----------->|peripheral |
|--------------| |------------- ------|

Now, for the microprocessors, this address usually is available on the memory device ( another memory IC ) interfaced with that microprocessor.
So, in order to locate the specific data, its address is put by the microprocessor (through the execution of the programme stored in microp. ) on the address bus.

Since, it's only the addresses on the memory devices or other peripherals interfaced with microp. need to be addressed hence address bus is unidirectional. That is the "address" flows from microp. to the interfaced device and not the other way. [ Since it is never required and never intended ].
On the other hand, once the "address" is located on the memory device, the "data" residing at that address needs to be either read back/stored to the microp. or a fresh/new data need to be written on that specific "address" (located by address bus). This job of reading or writing data is done by the data bus. While, in case of reading the data the data flow direction shall be from the interfaced memory or other peripheral to the microp., in case of writing it shall be reverse, i.e. from the microp. to the memory device hence, we need to have a bidrectional bus.

Therefore from above reason it is clear that why bus is unidirectional and bidirectional .

|--------------| |--------------------|
| microp. |-----------Data Write -------->| peripheral |
|--------------|<----------Data Read----------|------------- ------ |

Similar is the case with the control bus, where there are different status signals exchanged between the microp. and the interfaced device to the microp. hence it also needs to be bi-directional.

Note- terms used above -

1) microp- stands for microprocessor

2) IC - stands for integrated circuit