When thinking of simple programmable logic devices, we need to understand what programmable logic devices are. Logic devices are logic gates that take inputs and determine a binary output, based on that gate’s rule. There are many logic gates rules such as AND, NOR, OR and many more, and these logic gates are the decision-makers of a circuit. However, when changing the input information in a circuit, this usually would have to be completed as a physical task. This is where programmable logic devices differ, as these are devices that can be wiped and reprogrammed through software, rather than changing hardware. To define these even further, SPLDs are the least complicated forms of programmable logic devices.
In the case of an SPLD, these programmable devices will contain simple logic gates like AND or OR gates, and flip-flop components. They are then programmed using software and Hardware Description Language (HDL) and/or VHSIC (Very High-Speed Integrated Circuit) Hardware Description Language (VHDL). VDHL and HDL work similarly to coding language and instruct the logic devices how to perform. Coding language examples for SPLDs include CUPL, PALASM and ABEL.
Because SPLDs are a mixture of memory and logic devices, they retain their memory through the use of silicon anti-fuses, which is silicon within the circuit that has been modified to hold the memory. In the case of more volatile or simpler forms of memory, the input will have to be programmed every time, and this can be done automatically by an additional circuit.
The final type of SPLD available is Programmable Read-Only Memory or PROM.