Programmable logic array architecture

A Programmable Logic Array (PLA) is a type of digital logic device used to implement combinational logic circuits. PLAs can be configured to realize various logic functions by programming their connections. They consist of two main components: a programmable AND array and a programmable OR array. ### Architecture of Programmable Logic Arrays #### 1. **Inputs and Outputs** - **Inputs:** A PLA has multiple input lines. Each input can be connected directly to an AND gate or inverted (NOT). - **Outputs:** The output lines represent the final logic functions that the PLA implements. Outputs are generated from the programmable OR gates. #### 2. **Programmable AND Array** - The AND array consists of a series of AND gates. Each AND gate can be programmed to connect specific inputs (or their complements) to an output. - The number of AND gates can vary depending on the specific application and design requirements. #### 3. **Programmable OR Array** - The OR array takes the outputs from the AND array and combines them to produce the final outputs. - Similar to the AND array, the OR array consists of multiple OR gates, each of which can be configured to include specific AND gate outputs. #### 4. **Interconnect** - The connections between the input lines and the AND gates, as well as between the AND gates and the OR gates, can be customized through programming. This setup allows for a large number of possible logic combinations. ### Functionality - To configure a PLA for a specific logic function, the designer specifies which inputs should be connected to which AND gate, and which AND gates should be connected to which OR gate outputs. - This programming can be done using fuses or antifuses for creating permanent connections, or it can be accomplished using software in the case of FPGA (Field Programmable Gate Arrays), which have a more flexible architecture. ### Advantages of PLAs - **Flexibility:** They can be tailored to realize any desired logic function, making them versatile for a wide range of applications. - **Simplicity in Design:** They reduce the need for complex wiring since the logic can be implemented in a single device. - **Reduced Size:** Can replace multiple discrete components in a circuit. ### Disadvantages of PLAs - **Speed:** Generally slower than other dedicated hardware implementations like custom ASICs. - **Cost:** For small-scale production, PLAs could be more expensive than similar logic circuits in traditional discrete form. - **Power Consumption:** Depending on the implementation and number of active connections, they can have higher power consumption than fixed-function logic devices. ### Applications PLAs are used in various applications, including: - Implementing combinational logic functions. - Constructing interface circuits. - Custom logic solutions in consumer electronics, telecommunications, and automotive systems. In summary, a Programmable Logic Array provides a flexible means of implementing combinational logic through programmable connections, making it an important tool in digital circuit design.