TOPIC : Programming Model

1. TOPIC : Programming Model UNIT 1: Modeling Digital Circuits Module 1 : Functional Modeling

2. Programming model • All the combinational elements in a circuit can be represented in a programming model. • Any logic function is expressed in terms of basic logic operations namely • NOT • AND,NAND • OR,NOR • EXOR,EXNOR • Code based programs can be written for any digital circuit using the above operations. • Assembly coding is an example of programming model.

3. Example of programming model LDA A //Load A in accumulator XOR B // A xor B STA E // Store A xor B in E XOR C // A xor B xor C STA Sum // store it in Sum LDA E AND C STA F LDA A AND B STA G LDA F OR G STA Cout E F G

4. Register Transfer Language(RTL) Model • RTL- A kind of hardware description language (HDL) • It is used in describing the registers of a computer or digital electronic system, and the way in which data is transferred between them. • In computer, data words are stored in registers and memories are organized as arrays of registers. • For example : • register A[0:7] // A is a 8 bit register • memory M[0:7;0:255] // A 256 array of 8 bit register • RTLs provide models for systems at the register and instruction set levels.

5. RTL model • In this we make HDL models of registered circuits and how signals interact between them such as memories, flip flops, latches, shift registers, and so on. • RTL codes are fully synthesizable(can be realized in hardware), because they are written using basic HDL structures. • RTL models are characterized as functional, because they emphasize functional description while providing only summary about structural circuits.

6. Example of RTL model E = A XOR B F = E AND Cin G = A AND B S = E XOR Cin Cout = F OR G • Here A, B, Cin are input registers and Cout, S are the output registers. E, F, and G are intermediate registers E F G

7. RTL detail • Primitive operator : This describes the processing and transfer of data. Example C = A + B • Conditional operator : Control of data transformation. For example : if (x) then c = A + B • Case operator : This is used for multiway decision. Example : signal{X[0:1]} case 0 : C = A + B; ………. case 3 : C = A – B;