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8085 Microprocessor: De-multiplexing of AD0-AD7 Address and Data Lines

  De-multiplexing of AD0-AD7 of 8085 Microprocessor THE ADDRESS AND DATA BUSES: • 8085 Microprocessor have total 16 address lines and 8 data lines. • 8 signal lines A8 – A15 which are unidirectional. • The other 8 address bits are multiplexed with the 8 data bits. So, the bits AD0 – AD7 are bi-directional and serve as A0 – A7 (address bus) and D0 – D7 (data bus) at the same time. • During the execution of the instruction, these lines carry the address bits during the early part, then during the late parts of the execution, they carry the 8 data bits. In order to separate the address from the data, we can use a latch to save the value before the function of the bits changes. THE CONTROL AND STATUS SIGNALS: • There are 4 main control and status signals. 1. ALE (Address Latch Enable): This signal is a pulse that become 1 when the AD0 –AD7 lines have an address on them. It becomes 0 after that. This signal can be used to enable a latch to save the address bits from the AD lines. 2. RD ...
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Interrupts in 8085 Microprocessor: Vectored-Non Vectored Interrupts And Maskable-Non Maskable Interrupts

Vectored Interrupt: In vectored interrupts, the manufacturer fixes the address of the ISR to which the program control is to be transferred. the processor automatically branches to the specific address in response to an interrupt.  • The TRAP, RST 7.5, RST 6.5 and RST 5.5 are vectored interrupts. Non-Vectored Interrupt:   But in non-vectored interrupts the interrupted device should give the address of the interrupt service routine (ISR).    • The INTR is a non-vectored interrupt. Hence when a device interrupts through INTR, it has to supply the address of ISR after receiving interrupt acknowledge signal. Maskable & Non-Maskable Interrupt: The hardware vectored interrupts are classified into maskable and non-maskable interrupts.  • TRAP is non-maskable interrupt.  • RST 7.5, RST 6.5 and RST 5.5 are maskable interrupt. Masking is preventing the interrupt from disturbing the main program. When an interrupt is masked the processor will not accept the i...
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Interrupts in 8085 Microprocessor-Hardware Interrupt And Software Interrupt

What is Interrupt and how it is generated? Interrupt is a signal send by an external device to the processor, to the processor to perform a particular task or work. In the microprocessor based system the interrupts are used for data transfer between the peripheral and the microprocessor. When a peripheral is ready for data transfer, it interrupts the processor by sending an appropriate signal to the interrupt pin of the processor. If the processor accepts the interrupt then the processor suspends its current activity and executes an interrupt service subroutine to complete the data transfer between the peripheral and processor. After executing the interrupt service routine the processor resumes its current activity. This type of data transfer scheme is called interrupt driven data transfer scheme. Types Of Interrupt: The interrupts are classified into software interrupts and hardware interrupts. • The software interrupts are program instructions. While running a program, if a software ...
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