Core Tips for Electronic Enthusiasts : Programmable Array Logic (PAL) is a simple PLD. This article introduces the output structure of PAL and the naming rules of PAL devices from the electronic enthusiast network.
1. PAL output structure
Programmable Array Logic (PAL) is a programmable structure with item-programmable or item-fixed structure. In order to facilitate various logic structure functions, its output structure usually has many structures, and each structure has a class period. Corresponding to it. The following is a centralized output structure commonly used in combinatorial logic:
Fixed output structure
The fixed output structure is the simplest output structure in the programmable device. Its output is the output of the array or the function of the simple combinational logic circuit, as shown in the following figure:
Figure 1 fixed output structure
Asynchronous I/O output structure
The simple fixed output structure above can only implement a simple combinatorial logic function. If you want to realize that its output can be used both as an input and as an input, this is not possible with the above circuit, which requires To the asynchronous I / O output structure, as shown below:
Figure 2 asynchronous I / O output structure
It can be seen from the figure that when the enable terminal of the three-state gate is 0, its tri-state gate handles the high-impedance state, and its internal output is isolated from the I/O line. At this time, the I/O can be used as an input. When the use level of the tri-state gate is 1, its I/O is the output. At this time, the internal logic function not only outputs the I/O terminal, but also feeds back to its internal programming matrix, which can realize various requirements. The feedback circuit reduces the external connections of the circuit, such as the RS flip-flop circuit and various cascading circuits.
Output with XOR gate
The XOR gate is added to the output of the XOR gate. The addition of this XOR gate causes the circuit composition to change. If a logic function requires a large number of terms (such as a four-input function, its The number of items and items is up to 16). If the inverse function is used, it is found that the number of items is less than the number of items (which is 16 minus the number of items of the original function). The XOR gate has a characteristic: When one input of the input is 0, its output is equal to the other input; and when one of the inputs is fixed to 1, its output is the other input. The introduction of this XOR gate makes it possible to implement the function with the original function through the inverse function.
2. naming rules for PAL devices
The naming of the PAL device is related to its input and output pin count and output structure. The following figure shows its naming convention:
Siren Alarm,Outdoor Siren,Wireless Siren,Home Alarm Siren
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