* Question
What are extended product terms in the MAX7000S architecture?
* Answer
In the Altera MAX7000S CPLD architecture, the term extended product terms (or expander product terms) refers to an architectural feature that enhances the logic capacity of each macrocell by allowing additional product terms to be borrowed and shared.
Here’s a breakdown:
Background: Product Terms in CPLDs
In programmable logic devices, product terms are the ANDed combinations of input signals.
A macrocell typically combines a limited number of product terms (e.g., 4 or 5) through an OR gate to form logic functions.
Complex logic functions may require more product terms than a single macrocell natively provides.
Extended Product Terms in MAX7000S
Each macrocell in MAX7000S can borrow additional product terms from a common pool, called expander (or extended) product terms.
These extended product terms are routed into the macrocell’s OR gate, effectively increasing its logic capacity.
This allows designers to implement wider logic equations without having to split functions across multiple macrocells.
Key Functions
Logic Expansion
A macrocell with limited native product terms can attach additional product terms from the expander pool.
Flexibility in Design
Reduces the need for manual optimization or breaking equations into smaller pieces.
Makes it possible to fit larger state machines, arithmetic functions, or control logic into fewer macrocells.
Efficient Resource Utilization
Instead of wasting macrocells for overflow logic, the extended product terms provide a shared pool of extra logic resources.
Example
Suppose a macrocell has 5 dedicated product terms.
Your logic equation needs 8.
The macrocell can use its 5 + 3 extended product terms from the pool, implementing the entire equation within a single macrocell.
In summary:
In the MAX7000S architecture, extended product terms are shared, borrowable logic resources that allow each macrocell to go beyond its built-in product term limit. They enable more complex logic functions, optimize macrocell usage, and improve flexibility in fitting designs into the device.
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