Pins of 8259
In this article, we will go through the Pin diagram of 8259, first we will start our article with the definition of the 8259, then we will go through the pin diagram of 8259 in brief and we will go through each pin. We will go through different pins like Vcc, INT, RD, etc.
Table of Content
- What is 8259?
- Pin Diagram of 8259
- Pin Diagram Description of 8259
- Pins of 8259 – FAQs
What is 8259?
Intel 8259 is a programmable Interrupt Controller(PIC).By connecting intel 8259 with these microprocessors, we can increase their interrupt input sources into a single interrupt output. It is commonly used in older computer systems to manage interrupts from various devices. It typically has two main modes, the cascade mode, where multiple 8259 chips can be linked together to handle more interrupts, and the single mode, where only one chip is used.
Pin Diagram of 8259
Here is a description of the pins commonly found on the 8259.
8259 Pin Diagram
Pin Diagram Description of 8259
|
Symbol |
Pin No. |
Type |
Name and function of Pin |
|---|---|---|---|
|
Vcc |
28 |
Input(I) |
Supply : +5V supply |
|
GND |
14 |
i |
Ground |
|
CS* |
1 |
I |
Chip Select : A low on this pin enables RD* and WR* communication between the CPU and the 8259A. INTA functions are independent of CS. |
|
WR* |
2 |
I |
Write: A low on this pin when CS is low enables the 8259A to accept command words from the CPU. |
|
RD* |
3 |
I |
Read :When the CS pin is low, a low signal on this pin allows the 8259A to transfer status information onto the data bus for the CPU. |
|
D7-D0 |
4-11 |
I/O |
Bidirectional data bus : Information related to control, status, and interrupt vectors flows through this bus. |
|
CAS0-CAS2 |
12,13,15 |
I/O |
Cascade lines : The CAS lines from a private 8259A bus to control a multiple 8259A structure. These pins are outputs for a master 8259A and input for a slave 8259A. |
|
SP*/EN* |
16 |
I/O |
Slave program/Enable buffer: This is a dual function pin. When in the buffered mode it can be used as an output to control buffer transceivers(EN).When not in the buffered mode it is used as an input to designate a master(SP =1) or Slave(SP = 0). |
|
INT |
17 |
O |
Interrupt : This pin goes high whenever a valid interrupt request is asserted. It is used to interrupt the CU, thus it is connected to the CPU, thus it is connected to the CPU’s interrupt pin. |
|
IR0-IR7 |
18-25 |
I |
Interrupt Request : Asynchronous inputs. An interrupt request is executed raising an IR input(low to high), and holding it high until it is acknowledged(Edge triggered mode), or just by a high level on an IR input(Level Triggered Mode). |
|
INTA* |
26 |
I |
Interrupt Acknowledge: This pin is used to enable 8259A interrupt-vector data onto the data bus by a sequence of interrupt acknowledge pulses issued by the CPU. |
|
A0 |
27 |
I |
AO Address line : This pin acts in conjunction with the CS*, WR* and RD* pins. It is used by the 8259 to decipher various command words the CPU writes and status the CPU weighs to read. It’s usually linked to the CPU’s A0 address line (A1 for 8086, 8088). |
Conclusion
The 8259’s pins, including INT, CS and IR lines, manage efficiency. They prioritize requests via INTP, communicate with the CPU using WR and RD, and acknowledge and end interrupts with INTA and EOI. This flexibility allows for smooth handling of multiple interrupt sources.
However, hardware interrupt management can introduce complexities, especially in systems with numerous devices. Nonetheless, the 8259’s pins are essential for ensuring timely responses to peripheral events, enhancing system reliability. They enable the CPU to handle interrupts efficiently.
Pins of 8259 – FAQs
How does the Intel 8259 expand the interrupt input sources of microprocessors like the Intel 8086 and 8088?
The Intel 8259 can be connected with microprocessors such as the Intel 8086 and 8088 where multiple hardware interrupts from different devices can be connected together into a single interrupt output.
What are the main operational modes of the Intel 8259, and how do they function?
It operates on two modes which are single and cascade mode.In cascade mode multiple 8259 can be connected together which can handle more interrupts while in single mode only one chip is used.
How does the Intel 8259 communicate with the CPU?
Intel 8259 uses various pins to communicate between cpu such as WR* and RD* for writing and reading words, CS* for chip selection, and INTA* for interrupt acknowledgment.