近代数字计算机和其它电子设备中,除了标准的中、小规模集成电路、微处理器、存储器、成品的外围电路以外,还常常有一些专用的A SIC(application Specific integrated circuit)器件。在ASIC中,可编逻辑器件PLD(programmable logic device)是一类用户可自行编程的简便多用硬件。最早出现的PLD是双极型器件,它可进行一次编程,称为可编阵列逻辑PAL(programmable array logic)。简单的PAL是一个组合逻辑电路,它包含一个与阵和一个或阵,可实现“积之和表达式”描述的逻辑函数。PAL的与阵是可编的,而或阵是不可编的。图1所示的PAL10H8逻辑图中,或阵的各个或门已固定连好;与阵中的垂直线与输入信号的原码和反码相连, In modern digital computers and other electronic devices, in addition to the standard peripheral circuits of medium- and small-scale integrated circuits, microprocessors, memories and finished products, there are often some specialized application specific integrated circuits (AICs). In the ASIC, the programmable logic device PLD (programmable logic device) is a kind of user-programmable simple and versatile hardware. The earliest PLD was a bipolar device that could be programmed once, called programmable array logic (PAL). A simple PAL is a combinational logic circuit that contains a logic function that can be described with a matrix and an OR matrix that implements the “product sum expression.” PAL and array are editable, and or array is not editable. In the logic diagram of PAL10H8 shown in FIG. 1, the OR gates of the array are fixedly connected; the vertical lines in the array are connected with the original code and the inverted code of the input signal,