Tag Archives: microprocessor
Programmable Interrupt Controller 8258
Interrupts can be used for a variety of applications. Each of these interrupt applications requires a separate interrupt input. If we are working with an 8085 microprocessor we get TRAP, RST7.5, 6.5, 5.5 and INTR interrupts inputs. For applications where we have multiple interrupt sources we have to use external device called a priority interrupt controller (PIC). By connecting such a device it is possible to increase the interrupt handling capacity of the microprocessor. The 8259A is a commonly used priority interrupt controller, which is specifically designed for use with interrupt signals INTR and INTA of Intel series. It is packaged in a 28 pin DIP. It uses NMOS technology and requires a single +5V supply.
Features of 8259A
It can manage eight priority interrupts. This is equivalent to providing eight interrupt pins on the processor in place of INTR pin.
It is possible to locate vector table for these additional interrupts anywhere in the memory map. However, all eight interrupts are spaced at the interval of either four or eight locations.
By cascading nine 8259s it is possible to get 64 priority interrupts.
Interrupt mask register makes it possible to mask individual interrupts request .
It can be programmed to accept either the level of triggered or triggered interrupt request.
With the help of this user can get the information of pending interrupt in service interrupts and mask interrupts.
The 8259 A is designed to minimize the software and the real time overhead handling multilevel priority interrupts.
Interfacing Multiplexed Display
To solve the problems of the static display approach, multiplexed display method is used. Here 4 seven segment displays connected using multiplexed method. Here common anode seven segment LEDs are used. Anodes are connected to +5V through transistors. Cathodes of all seven segments are connected in parallel and then to the output of 7447 IC through resistors. The PNP transistors connected in series with the common anode of each digit act as an ON and OFF switch for that digit. Here is how the multiplex process works.
In multiplexed display, the segment current is kept in between 40mA to 60 mA. So that they will appear as they would if not multiplexed. Even with this increased segment current, multiplexing gives a large saving in power and hardware components.
