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Why higher order address bus not multiplexed with data bus of 8085?
The higher order address bus is not multiplexed with data bus of 8085 because that is the way Intel designed the processor. Besides, the data bus is only 8 bits and the address bus is 16 bits. If you were to multiplex the whole address bus on the data bus, you would need two T1 (ALE) states, and that would be excess logic. Back to the original answer - that is simply the way Intel designed the processor.
How do you demultiplex address and data bus?
In order to demultiplex the address and data bus, you provide latches that sample the multiplexed bus. At ALE=true, they follow the bus. At ALE=falling edge, they lock onto the last value of the bus. The latches will then become the address bus, while the original bus becomes the data bus.
Why data bus is bidirectional bus in Intel 4004?
A data bus is bidirectional because the processor needs it to both read and write. Also, in the case of the 4004, the data bus was tri-multiplexed with the 12 bit address bus and the 8 bit opcode bus.
Why 4 bit address bus is grounded?
The data bus in the 8086 is 16 bits in size, while the address bus is 20 (16bits would only address 64KB of memory, an extra 4 bits allows to address the total of 1MB, this is done trough segmentation of the memory). To form a multiplexed of data bus and address bus, four bits of 8086 address bus are grounded.
What is meant by multiplexed address data bus?
Multiplexing of the data and address buses is done to reduce the pin count on the microprocessor chip. The address information is emitted at the beginning of a memory cycle, and external logic is expected to latch that address. Then the bus becomes the data bus and the required data is transferred to or from memory using the latched address.In the 8085, this saves 8 pins at the cost of 1 pin, ALE. In the 8086/8088, this saves 16 pins at the cost of 1 pin, ALE. In some architectures or modes, there is no ALE, but the external logic is still required to know when to latch the address based on some other criteria.As an example of that, in the original Intel 4004, the microprocessor's bus was 4 bits, while the address bus was 12 bits. There were 8 clock cycles. In the first three, external logic was expected to latch the three 4 bit parts of the 12 bit address. Similarly, in the next two, the resultant opcode, which as 8 bits, was multiplexed by the external logic into two 4 bit parts. (The 4004 was only a 16 pin chip, but it packed a lot of complexity in its day, being the world's first microprocessor.)
How are the data bus and address bus are demultiplexed?
The data and address buses are multiplexed in order to save pin count on the chip. In the first clock cycle of a read or write cycle, the address is emitted on the address/data bus. The ALE signal is used to strobe the address, after which the address/data bus becomes the data bus. External logic is expected to strobe the address at the trailing edge of ALE. ALE is generated directly by the 8085, and by the 8086/8088 in minimum mode. In maximum mode in the 8086/8088, ALE is generated by the 8288 Bus Controller.
What are the disadvantages of multiplexed address and data bus?
The primary disadvantage of a multiplexed address and data bus is that it requires additional time to transmit both address and data signals, leading to reduced overall data transfer rates. This design can also complicate circuit design and timing, as the bus must switch between address and data modes. Furthermore, the need for demultiplexing adds complexity and potential for timing errors, which can affect system performance and reliability. Lastly, multiplexing can limit the maximum addressable memory space compared to dedicated buses.
ALE in detail 8086 microproccesor?
The ALE (Address Latch Enable) signal in the 8086 microprocessor is used to demarcate the time when the address bus is valid. It indicates that the multiplexed address/data bus (AD0-AD15) is carrying a valid address during the first part of a bus cycle. When ALE is asserted, external latches can capture and hold the address, allowing the data bus to later carry data without confusion. This functionality is crucial for enabling the proper interfacing of the 8086 with memory and peripheral devices.
Explain the need to demultiplex the bus AD7-AD0 in 8085 microprocessor?
The AD0-AD7 lines in an 8085 are multiplexed to reduce the pin count of the IC. Several added features were added to the 8085 from the 8080 design, and Intel did not want to require a larger package.
What Are the Types of Buses in a Computer?
There are 2 kinds Data bus and address bus data bus which carries the data ( includes both instruction and data). address bus which carries where the data in the data bus must be sent to in the RAM or which I/O device has to be active to read / write data to the data bus .
How is demultiplexing done in 8085 microprocessor?
it is nothing
Why is data bus bidirectional but address bus unidirectional?
The address bus is unidirectional becos address information is always given by microprocessor to i/o devices. The data bus is bidirectional bcos it takes the data from other devices & also give the data to other i/o devices
