programmable array logic - flexibility and high speed at (relatively) low cost

programmable array logic elektor may 1985 It is well known that programmable ROMs (read-only memories) can be used not only as a logic building brick, but also as a Boolean operator or complex encoder. For some years now, there has been a better, more flexible, and, last but not least, cheaper alternative to the usual bipolar PROM (programmable ROM): PAL (programmable array logic), not to be confused with the widely used colour television system of the same name (or rather, acronym), or with PLA (programmable logic array). programmable array logic flexibility and high speed at (relatively) low cost A PAL device is basically a matrix with the same logic arrays as PROMs and PLAs, but, whereas PROMs use fixed AND arrays and programmable OR arrays, and PLAs use programmable AND arrays and pro- grammable OR arrays, the PAL uses pro- grammable AND arrays and fixed OR arrays. In all three types of device, the AND array outputs feed the OR arrays. The PLA provides the greatest flexibility...