EP220 ALTERA [Altera Corporation], EP220 Datasheet - Page 4

• Manufacturer Part Number: EP220
• Description: Classic EPLDs
• Manufacturer: ALTERA [Altera Corporation]

EP220 & EP224 Classic EPLDs
Figure 2. EP220 & EP224 Macrocell
4
Pin, I/O, and
Macrocell Feedback
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
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.
Figure
2.
Output Enable
Feedback to
Logic Array
Inversion
Control
CLK
Feedback
Select
Programmable
Register
D
Q
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