General  Description
The Altera® a8259 MegaCore™ function is a programmable interrupt  controller. The a8259 can be initialized by the microprocessor through  eight data bus lines (din[7..0] and dout[7..0]), and the ncs, nrd, nwr,  int, and ninta control signals. Figure 1 shows the symbol for the a8259.

Features
■ Optimized for FLEX® and MAX® architectures
■ Offers eight levels of individually maskable interrupts
■ Expandable to 64 interrupts
■ Offers a flexible priority resolution scheme
■ Provides programmable interrupt modes and vectors
■ Uses approximately 399 logic elements (LEs) in FLEX devices
■ Functionally based on the Intel 8259 device, except as noted in the   “Variations & Clarifications” section on page 79