Digital Electronics: Principles, Devices and Applications

Programmable Logic Devices 321InputsProducttermsHard-wiredOR-ArrayProgrammableAND-ArrayOutputsFigure 9.18Generalized PAL device.ABCDACDLogic'0'Figure 9.19Programmability of inputs in a PAL device.letter indicates the number of outputs. In the case of PAL devices offering a combination of differenttypes of logic output, the rightmost number indicates the number of the output type implied by theletter used in the designation. For example, a PAL device designated PAL-16L8 will have 16 inputsand eight active LOW outputs. Another PAL device designated PAL-16R4 has 16 inputs and fourregistered outputs. Also, the number of inputs as given by the number designation includes dedicatedinputs, user-programmable inputs accessible from combinational I/O pins and any feedback inputs