ROM, PROM & PLA/FPGA Look-Up Tables
ROM (Read-Only Memory) is a non-volatile memory storing permanent data, while PROM (Programmable ROM) allows one-time programming by users. PLA (Programmable Logic Array) and FPGA (Field-Programmable Gate Array) use configurable logic blocks, often implemented as look-up tables (LUTs), to perform custom logic functions. These components are essential in digital electronics for data storage, logic implementation, and enabling reconfigurable computing architectures.
ROM, PROM & PLA/FPGA Look-Up Tables
ROM (Read-Only Memory) is a non-volatile memory storing permanent data, while PROM (Programmable ROM) allows one-time programming by users. PLA (Programmable Logic Array) and FPGA (Field-Programmable Gate Array) use configurable logic blocks, often implemented as look-up tables (LUTs), to perform custom logic functions. These components are essential in digital electronics for data storage, logic implementation, and enabling reconfigurable computing architectures.
💡 Key Takeaways
- Understand ROM, PROM, PLA, and FPGA LUT basics and how they differ in purpose and programmability.
- Learn how ROM stores fixed data and how PROM enables one-time programmable data or truth tables.
- Understand how a PLA uses a programmable AND-OR network to implement combinational logic from a truth table.
- Explore FPGA LUTs as configurable logic blocks that implement arbitrary Boolean functions via small truth tables and how they connect to form larger circuits.
- Compare trade-offs among fixed vs programmable memory, speed, area, and reuse in firmware vs logic design.
❓ Frequently Asked Questions
What is ROM and how does it differ from PROM?
ROM stores fixed data programmed during manufacture; PROM is blank at production and can be programmed once (typically by fusing links). After programming, PROM data is read-only and non-volatile.
What is PROM and how is it programmed?
PROM stands for Programmable Read-Only Memory. It is manufactured blank and programmed once by creating or destroying fuses/antifuses, permanently encoding the data.
What is a PLA (Programmable Logic Array) and how is it used?
A PLA is a programmable logic device with a programmable AND (product-term) array and a programmable OR (sum) array to realize combinational logic networks. It was an early way to implement custom logic before FPGA-era architectures.
What is an FPGA and what role do LUTs play inside it?
An FPGA is a Field-Programmable Gate Array—an IC whose logic and interconnect are reconfigurable. LUTs (Look-Up Tables) inside FPGA cells implement small boolean functions by storing a truth table that maps inputs to outputs.
What is a Look-Up Table (LUT) in digital design?
A LUT is a small memory that outputs a value for every combination of its inputs, effectively implementing a boolean function. In FPGAs, LUTs typically handle 4–6 inputs and can be cascaded to realize larger functions.