Ao of the A is connected to system line Al. The data lines of an are connected to the lower half of the system data bus; because the expects to receive interrupt types on these lower eight data lines. The eight IR inputs are available for interrupt signals. Cascading : The can be easily interconnected to get multiple interrupts. Fig below shows how can be connected in the cascade mode. In cascade mode one is configured in Master mode and other should be configured in the Slave mode.

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Draw Circuit for keyboard interfacing with ? For interfacing to the microprocessor system, usually push buttons keys are used. Whenever a key is pressed, there are small mechanical vibrations that cause noise on the input, which can cause the microprocessor to detect several keypresses instead of just one.

Bouncing happens because of the tendency of any two metal contacts in an electronic device to generate multiple signals as the contacts close or open. You can solve this problem using software or hardware debouncing. The hardware approach is shown in figure 8. The software routine to get key code with key debounce is: In the technique shown in figure 8. This means, to interface one key,one input line is required. This is the disdavantage as it requires many line as many keys.

This number of lines required can be reduced if keys are put in matrix form. The figure 8. The connection will be made such that when a key is pressed, it shotrs the corresponding one row and one column.

Two ports are required, input port for connecting rows and and output port for connecting columns. The lines connected to rows are called returned lines and the lines connected to columns are called scan lines When all a key is pressed it shorts the corresponding row and column. If the output line of this colummn is low, then it makes the corresponding row line low,other wise the status of row line will be high.

The pressed key will be identified by the data sent on the oputput port and the input code received from the input port. Figure 8. The is being used in maximum mode and port A of is used for columns and port B for rows. By making use of the lookup table stored in the memory, the microprocessor will determine the code of the depressed key, then it will initiate the action.

Is it possible to interface more than 64K memory using ? In order to interface more than 64K of memory using the , you would need an external address register, perhaps maintained by the , which contained an offset register for part of the memory address space.


Interface 8255 with 8085 microprocessor for addition

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.


Programmable peripheral interface 8255

Microcontroller Microprocessor The Intel is programmable Interval Timers PTIs designed for microprocessors toper form timing and counting functions using three bit registers. Each counter has 2 input pins, i. To operate a counter, a bit count is loaded in its register. On command, it begins to decrement the count until it reaches 0, then it generates a pulse that can be used to interrupt the CPU. Features of It has three independent bit down counters.


Interfacing 8253 (Timer IC) with 8085 Microprocessor



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