Designing a Basic Computer Architecture: Key Components and Control Logic Explained
This lecture delves into the design of a basic computer system, covering critical components such as the 16-bit memory unit, registers, flip-flops, decoders, and control logic gates. Understanding the operation of the memory unit, register control signals, and Boolean expressions that define control functions is essential for designing effective computer architecture. The lecture includes practical examples of register transfer operations and the logic required to manage data flow within the computer. Assignment questions allow for hands-on application of concepts discussed.
Designing a Basic Computer Architecture: Key Components and Control Logic Explained
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Presentation Transcript
Lecture#11 M. Mateen Yaqoob The University of Lahore Spring 2014
Design of a basic computer • The basic computer consists of: • Memory unit with 4096 (4KB) words of 16 bits each • Nine registers: AR, PC, DR, AC, IR, TR, OUTR, INPR and SC • Seven flip-flops: I, S, E, R, IEN, FGI and FGO • Two decoders: 3x8 operation decoder and 4x16 timing decoder • 16-bit common bus • Control logic gates • Adder and logic circuit connected to the input of AC • The memory unit is a standard component that can be obtained readily from a commercial source
Control logic gates • Input comes from the two decoders and bits 0 through 11 of IR • The other inputs are; • AC bits 0 through 15 to check if AC=0 and to detect the sign bit in AC(15) • DR bits 0 through 15 to check if DR=0 • the values of seven flip-flops • The outputs of control logic circuit are: • Signals to control the input of nine registers • Signals to control the read and write inputs of memory • Signals to set, clear, or complement the flip-flops • Signals for S2, S1 and S0 to select a register for the bus • Signals to control the AC adder and logic circuit
Control of register and memory • Control inputs of registers are LD (load), INR (increment), and CLR (clear) • First three statements specify transfer of information from a register or memory to AR • The content of source register or memory is placed on bus and content of bus is transferred into AR by enabling its LD control input • Fourth statement clears AR to 0 • Last statement increments AR by 1
Control functions can be combined into three Boolean expressions as: • The read operation is recognized by symbol M[AR]
Control of common bus • 16-bit common bus is controlled by selection inputs S2, S1 and S0.
Each binary number is associated with a Boolean variable X1 to X7, corresponding to gate structure that must be active in order to select register or memory for bus • When X1-1 the value of S2S1S0 must be 001 and output of AR will be selected for the bus • Table 5-7 is recognized as truth table for binary encoder • Boolean functions for encoder are:
To determine the logic for each encoder input, it is essential to find the control function which place the corresponding register onto the bus • For example, to find the logic that makes x1=1, we scan all register transfer statements and extract those statements that have AR as source • Boolean function of X1 is:
The logic gate that generates X7 must also be applied to read input of memory • So, the Boolean function for X7 is same as the one derived previously for read operation • In similar manner we can determine logic gate for other registers
Assignment • Perform question number 5-15 and 5-16 • Due Date: 14-07-2014
