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Altera Corporation

EP220 & EP224 Classic EPLDs

Macrocells

Each macrocell includes a product-term block with 8 AND product terms

feeding an OR gate. One product term is dedicated to the Output Enable

(OE) control of the tri-state buffer. The global logic array allows each

product term to connect to the true or complement of each input—36

inputs for the EP220, 44 inputs for the EP224—and I/O feedback signal.

See Figure 2.

Figure 2. EP220 & EP224 Macrocell

Macrocells can be individually configured for registered or combinatorial

operation, providing a mixed-mode operation not available in fixed-

architecture PAL devices. When registered output is selected, feedback

from the register to the logic array bypasses the output buffer. When

combinatorial output is selected, feedback comes from the I/O pin

through the output buffer, and can be used for bidirectional I/O. Unlike

PAL and GAL devices, all eight outputs on the EP220 and EP224 allow a

combinatorial feedback signal from the I/O pin to feed the logic array.

Data is clocked into the macrocell’s D register on the rising edge of the

global Clock.

Feedback

Select

DQ

CLK

Inversion

Control

Programmable

Register

Output Enable

Feedback to

Logic Array

Pin, I/O, and

Macrocell Feedback