Getting Started With Programmable Logic Devices,the 16v8 And 20v8

GETTING STARTED WITH PROGRAMMABLE LOGIC DEVICES, THE 16V8 AND 20V8 © Robert G. Brown All Rights Reserved August 25, 2000 Alta Engineering 58 Cedar Lane New Hartford, CT 06057-2905 (860) 489-8003 www.alta-engineering.com [email protected] 1 Hands on Design with Programmable Logic Devices The introduction of programmable logic devices (PLDs) was a great boon to the field of digital hardware design. The second generation PLD, the GAL (which stands for Generic Array Logic, a trademark of Lattice Semiconductor) is particularly suited for the small scale hardware designer. GALs offer the following benefits to the hardware designer: Flexibility - GALs are very flexible devices, they can implement both combinatorial logic functions (AND, OR, NAND etc.) and registered logic functions (counters, shift registers etc.) on the same chip. PAL replacement- The GAL16V8 and GAL20V8 each can directly replace over 20 of the common PAL (Programmable Array Logic - the first generation PLD) types each. This means you only need to stock 2 GAL types to handle your PLD needs. Space savings - In my experience each GAL has typically replaced between 2 and 4 standard TTL chips, saving a large amount of board space. Speed - GALs are fast devices with propagation delay down as low as 7 ns. Typical GALs have a propagation delay of only 15 ns - faster then standard 7400 or 74LS series logic. Reprogrammability - Not only are GALs programmable giving the ability to correct design errors and make board layout easier, they can be reprogrammed up to 100 times. Erasing and programming takes only a few seconds. Cost - In addition to the savings in PC board real estate, standard speed GAL16V8s and GAL20V8s (25 and 15 ns) cost only a few dollars even in small quantities. There are several varieties of