GAL stands for "Generic Array Logic." It is a type of programmable logic device (PLD) that belongs to the category of complex programmable logic devices (CPLDs). GALs are used for digital logic design and implementation in various electronic applications. Here's an overview of GALs:
- Functionality: GALs are programmable devices that contain an array of configurable logic cells, input/output pins, and interconnect resources. They allow users to create custom digital logic circuits by programming the connections and behavior of these cells.
- Logic Cells: A GAL's logic cells are programmable building blocks that can be configured to perform specific logic functions. These functions include basic Boolean operations, sequential logic, and even more complex tasks.
- Programming: GALs are programmed using hardware description languages (HDLs) like VHDL or Verilog, or through schematic capture software. The programming defines the connections between logic cells, effectively designing the desired logic circuit.
- Applications: GALs are used for various tasks such as state machine implementation, bus interfacing, glue logic, and more. They are particularly suitable for designs of moderate complexity that don't require the full resources of an FPGA.
- Architecture: GALs have a fixed internal architecture that is determined during fabrication. This contrasts with some other PLD types like FPGAs, which allow for more flexible and fine-grained customization.
- Fuse-Based Programming: Historically, GALs were programmed by blowing fuses to create the desired connections. Later versions adopted flash or EEPROM-based programming, enabling reprogramming without needing physical alterations.
- Advantages: GALs offer a good balance between customization and complexity. They are simpler to program and use than FPGAs, making them suitable for simpler designs where FPGA resources might be excessive.
- Disadvantages: GALs have limitations in terms of logic capacity compared to FPGAs, which might restrict their use in larger or more complex designs.
- Obsolete: While GALs were popular in the past, they have become less common due to the advancement of technology and the prevalence of FPGAs, which offer more flexibility and performance.
In summary, a GAL is a type of programmable logic device that allows users to create custom digital logic circuits. While they have certain limitations compared to more advanced devices like FPGAs, they remain relevant in specific scenarios where moderate complexity and cost-effectiveness are key considerations.