Application of PLD devices

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10.4 Application of PLD Devices

10.4.1 Programmable Device Development System

10.4.2 ABEL Hardware Description Language

First, the structure of the ABEL source file

Second, the basic grammar of ABEL

10.4.3 Application examples

10.4 Application of PLD Devices

10.4.1 Programmable Device Development System

10.4.2 ABEL Hardware Description Language

First, the structure of the ABEL source file

See an example of a simple ABEL source file.

Module G_3AND

Title' This is an example of 3 _input AND gate useing a GAL16V8'

"devICe type;

3 _AND device'GAL16V8';

"input PINs;

A, B, C pin 2, 3, 4;

"output pins;

Y pin 18;

"constants;

1,0=H,L;

Equations

Y=A&B&C;

Test_vectors([A,B,C]->[Y])

[0,0,0]一>[0];

[0,0,1]一>[0];

[0,1,0]一>[0];

[0,1,1]->[0];

[1,0,0]一>[0];

[1,0,1]一>[0];

[1,1,0]一>[0];

[1,1,1]一>[1];

End

1. Title segment

The title statement is an optional statement, and ABEL does not process the statement at compile time. format:

Module (string)

Title '(string)'

2. Definition segment

(1) Device definition: used to determine the device used. The statement format is:

(device serial number) device' device name';

Such as: U1 device 'GAL16R8'; it defines the device with the serial number U1 is GAL16R8.

(2) Signal and pin and pin type definition: Specify the signal name and its corresponding device pin, and explain the signal properties. The statement format is:

[! ] signal name, [! ] Signal name,...[! ] signal name pin pin number, pin number, ... pin number

[istype' attribute'];

(3) Constant definition: The constant identifier used to define the designer's habits replaces some special constant identifiers in the ABEL language. The statement format is:

Identifier, identifier, ... = constant, constant, ...;

Such as: 1,0,X,CP=H,L,.X.,.C.;

(4) array definition and expression definition

An array definition is a shorthand for a set of array elements with an identifier. Its statement format is:

Identifier = [element 1, element 2, ...];

Such as: S = [ Q1, Q2, Q3];

(5) Comment line: A comment added for easy reading. The compiler does not handle it.

Such as: "input pin; (input pin)

"output pin; (output pin)

3. Logic description segment --- the core of programming

(1) Logical equations. Its format is:

Equations

Equation 1;

Equation 2;

...

Equation n ;

(2) The truth table. Its format is as follows:

Truth _ table

([element 1, element 2...] -> [element 1, element 2,...])

[×, ×,...]——>[×,×,...]

...

[×. ×,...]——>[×,×,...];

The first line is the keyword, there is no semicolon after it, the second line is the header, enclosed in parentheses, and there is no semicolon. The left side of the parentheses is the input signal array, and the right side is the output signal array. The two arrays are connected by an assignment number. For combinatorial logic, the assignment number is "->", and for trigger output, the assignment number is ":>". Below the header is the truth table, with each line of the table as a statement, ending with a semicolon. Keywords and headers can also be written on the same line, but spaces and headers should be separated by spaces. The elements in the input and output arrays can be variable identifiers (such as [A, B, C]), array identifiers (such as [A, FF]), and FF = [Q2, Q1, Q0], That is, arrays can be nested in arrays.

4. Test vector segment --- Is the logic function of the test circuit correct?

The structure is as follows:

Test _ vectors

([element 1, element 2,...] ->[element 1, element 2,...])

[×,×,...]——>[×,×,...];

...

[×,×...]——> [×,×,...];

5. End segment

At the end of the module design, the end with the keyword end is indicated. Therefore end only corresponds to the module. There is no semicolon after end.

The typical structure of an ABEL source file is given below.

Module (string)

Title'(string)'

(string) device' (device name)';

[! ] signal name, [! ] signal name,...,[! ] signal name pin pin number, pin number, ..., pin number;

Identifier, identifier, ... = constant, constant, ...;

Equations

Equation 1;

Equation 2;

...

Equation n;

Test _ vectors([input signal]>[output signal])

End

Second, the basic grammar of ABEL

l. legal characters and statements

2. Identifiers and keywords

3, constants and values

4. Operator

5. Array and its operations

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