The A0 input of the A is used to select one of the two internal addresses in the device: A0 of the A is connected to system line A0. So the system addresses for the two internal addresses are F0H and F1H. The eight IR inputs are available for interrupt signals. Note : Unused IR inputs should be tied to ground so that a noise pulse cannot accidentally cause an interrupt. The A0 input of the A is used to select one of the two internal addresses in the device. A0 of the A is connected to system line A1.

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There are 5 hardware interrupts and 2 hardware interrupts in and respectively. But by connecting with CPU, we can increase the interrupt handling capability. For example, Interfacing of and increases the interrupt handling capability of microprocessor from 5 to 8 interrupt levels.

It can be programmed either in level triggered or in edge triggered interrupt level. We can masked individual bits of interrupt request register. We can increase interrupt handling capability upto 64 interrupt level by cascading further PIC. Clock cycle is not required. Other pins use are explained below. It takes the control word from the let say microprocessor and transfer it to the control logic of microprocessor.

Also, after selection of Interrupt by microprocessor, it transfer the opcode of the selected Interrupt and address of the Interrupt service sub routine to the other connected microprocessor.

The data bus buffer consists of 8 bits represented as D0-D7 in the block diagram. Thus, shows that a maximum of 8 bits data can be transferred at a time. This block is responsible for the flow of data depending upon the inputs of RD and WR. These two pins are active low pins used for read and write operations. Control logic — It is the centre of the microprocessor and controls the functioning of every block. If is enabled, and the other microprocessor Interrupt flag is high then this causes the value of the output INT pin high and in this way responds to the request made by other microprocessor.

Interrupt request register IRR — It stores all the interrupt level which are requesting for Interrupt services. Interrupt service register ISR — It stores the interrupt level which are currently being executed.

Interrupt mask register IMR — It stores the interrupt level which have to be masked by storing the masking bits of the interrupt level. Priority resolver — It examines all the three registers and set the priority of interrupts and according to the priority of the interrupts, interrupt with highest priority is set in ISR register. Also, it reset the interrupt level which is already been serviced in IRR. Cascade buffer — To increase the Interrupt handling capability, we can further cascade more number of pins by using cascade buffer.

So, during increment of interrupt capability, CSA lines are used to control multiple interrupt structure.


Microprocessor - 8257 DMA Controller

It is designed by Intel to transfer data at the fastest rate. Then the microprocessor tri-states all the data bus, address bus, and control bus. Each channel has bit address and bit counter. Each channel can transfer data up to 64kb. Each channel can be programmed independently. Each channel can perform read transfer, write transfer and verify transfer operations. It generates MARK signal to the peripheral device that bytes have been transferred.


8255A - Programmable Peripheral Interface

It transfers the opcode of the selected interrupts and address of ISR to the other connected microprocessor. It can send maximum 8-bit at a time. This block is used to flow the data depending upon the inputs of RD and WR. These are active low pins for read and write. Control Logic It controls the functionality of each block. It has pin called INTR.

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