Programmable Logic Devices
321
Programmable
AND-Array
Outputs
Inputs
Hard-wired
OR-Array
Product
terms
Figure 9.18 Generalized PAL device.
C
D
B
A
ACD
Logic'0'
Figure 9.19 Programmability of inputs in a PAL device.
letter indicates the number of outputs. In the case of PAL devices offering a combination of different
types of logic output, the rightmost number indicates the number of the output type implied by the
letter used in the designation. For example, a PAL device designated PAL-16L8 will have 16 inputs
and eight active LOW outputs. Another PAL device designated PAL-16R4 has 16 inputs and four
registered outputs. Also, the number of inputs as given by the number designation includes dedicated
inputs, user-programmable inputs accessible from combinational I/O pins and any feedback inputs