Unit-3 - Memory, ADC, Seq. Ckt, Comp Org..pptx

ELE101: Fundamentals of Electrical

and

Electronics Engineering

Sequential Logic Circuits

2



Combinational Logic Circuits

 _{Output is a function of the inputs}

only.

 _{Do not have “history”}



Sequential Logic Circuits

 Output is a function of the inputs and

the present state.

 Have “history”

 _{Maintain state information}

Sequential Logic Circuits

Basic Memory Elements

4



Latch

 Clock input is level sensitive.

 _{Output can change multiple times during}

a clock cycle.

 _{Output changes while clock is active.}



Flip Flop

 _{Clock input is edge sensitive.}

 _{Output can change only once during a}

clock cycle.

SR Latch (NOR)

5

Q_a

Q_b

SR Latch (NAND)

Gated SR Latch

7

S'

Gated D Latch

8

S'

R' S

Latches: Symbols

9

Memory

11

 _{Memory is required to store:}

1. data

2. application programs 3. operating system

 Can be broadly classified as:

Random Access Memory (RAM) or

Random Access Memory

(RAM)

12

 Can be written to or read from.

 Read/Write memory

 Reading from RAM is non-destructive.  Access time to read from any memory

location is the same.

 _{As compared to serial access memory.}

 Volatile

 Information is lost when power is

Random Access Memory

(RAM)

13



Static Random Access Memory (SRAM)

 _{Based on the Flip-Flop}

 _{Requires a large number of}

transistors

 _Fast



Dynamic Random Access Memory

(DRAM)

 _{Uses a single transistor to store}

charge

 _{Requires very few transistors}  Must be periodically refreshed

Random Access Memory

14



Address

 Location in memory of the binary

information

 Must be decoded to select the

appropriate location and read/write the associated data

 k-bit address → 2k _{memory locations}



Data

 _{Binary information of interest}

 Stored in a specific location in the

memory

Random Access Memory

15

address

10-bit address 1024 locations

Random Access Memory

Random Access Memory

17



Rather than use the

Read

and

Write

signals, most commercially available RAM

chips use Enable and Read/Write'



Enable

 _{Used to enable the selected RAM}

chip

 _{Aka. “chip select”}



Read/Write'

Read Only Memory (ROM)

18



Can only be read from.



Memory is written (or “programmed”)

once



Reading from ROM is non-destructive.

Access time to read from any memory

location is the same.

 _{As compared to serial access}

memory.



Non-Volatile

 Information is retained even after

Read Only Memory (ROM)

19



Programmable Read Only Memory (PROM)

 _{Can be “programmed”}



Erasable PROM (EPROM)

 Can be “programmed” and erased



Electrically Erasable PROM (EEPROM)

 Can be erased using an electrical

signal



UV Erasable PROM (UVEPROM)

Read Only Memory

20



ROM store “permanent” binary

information

 _{One-time programmable memory}

 _{Multiple-time programmable memory}



Address and Data

 _{k address bits}  _{n data bits}



2

x n ROM includes

 _k-to-2k _decoder

Read Only Memory

Read Only Memory

Read Only Memory

23



EEPROM (E

PROM)

 _{Electrically Erasable Programmable}

ROM



Flash ROM

 Similar to E2PROM

 Has additional circuitry to selectively

erase and program the memory in-circuit

Analog Signals

Analog signals – directly measurable

quantities in terms of some other quantity

Examples:



Thermometer – mercury height rises as

temperature rises



Car Speedometer – Needle moves farther

right as you accelerate



Stereo – Volume increases as you turn the

Digital Signals

Digital Signals – have only two states. For

digital computers, we refer to binary states,

0 and 1. “1” can be on, “0” can be off.

Examples:



Light switch can be either on or off

Examples of A/D Applications



Microphones -

waves in the air and convert them into varying electrical signals



Strain Gages -

(change in dimensions) when a stress is applied



Thermocouple –

converts thermal energy to electric energy



Voltmeters

BLOCK DIAGRAM

Analog



Digital Conversion

2-Step Process:



Quantizing - breaking down analog value is a

set of finite states



Encoding - assigning a digital word or number

Step 1: Quantizing

Example:

You have 0-10V

signals. Separate

them into a set of

discrete states with

1.25V

increments.

(How did we get

1.25V? See next

slide…)

Output

Quantizing

The number of possible states that

the converter can output is:

N=2

where n is the number of bits in the AD

converter

Example: For a 3 bit A/D converter,

N=2

=8.

Analog quantization size:

Encoding



Here we assign

the digital value

(binary number)

to each state for

the computer to

read.

Output

States Output Binary Equivalent

Accuracy of A/D Conversion

There are two ways to best improve

accuracy of A/D conversion:



increasing the resolution which improves

the accuracy in measuring the

amplitude of the analog signal.



increasing the sampling rate which

Resolution

 Resolution (number of discrete values the

converter can produce) = Analog Quantization size (Q)

(Q) = Vrange / 2^n, where Vrange is the range of analog voltages which can be represented

 limited by signal-to-noise ratio (should be around

6dB)

 In our previous example: Q = 1.25V, this is a high

resolution. A lower resolution would be if we used a 2-bit converter, then the resolution would be

Aliasing



Occurs when the input signal is changing

much faster than the sample rate.

For example, a 2 kHz sine wave being

sampled at 1.5 kHz would be reconstructed

as a 500 Hz (the aliased signal) sine wave.

Nyquist Rule:



Use a sampling frequency at least twice as

Overall Better Accuracy



Increasing both the sampling rate and the

A/D Converter Types



Converters

 Flash ADC

 Delta-Sigma ADC

Flash ADC



Consists of a series of comparators, each

one comparing the input signal to a unique

reference voltage.



The comparator outputs connect to the

How Flash Works



As the analog input voltage exceeds the

reference voltage at each comparator, the

comparator outputs will sequentially

saturate to a high state.



The priority encoder generates a binary

Accumulator(AC) : takes input from ALU

o_{The ALU takes input from DR, AC and INPR :} oADD DR to AC, AND DR to AC

Note) Input register is not connected to the bus. The input register is connected only to the ALU

Computer Registers

 Data Register(DR) : hold the operand(Data) read from

memory

 _{Accumulator Register(AC) : general purpose processing}

register

 _{Instruction Register(IR) : hold the instruction read from}

memory

 _{Temporary Register(TR) : hold a temporary data during}

processing

 _{Address Register(AR) : hold a memory address, 12 bit}

Computer Registers



Program Counter(

PC

) :

 hold the address of the next instruction to be read

from memory after the current instruction is executed

 _{Instruction words are read and executed in}

sequence unless a branch instruction is encountered

 _{A branch instruction calls for a transfer to a}

nonconsecutive instruction in the program

 The address part of a branch instruction is

transferred to PC to become the address of the next instruction

 _{To read instruction, memory read cycle is initiated,}

IR and TR



The instruction register, IR, can only be

loaded; it cannot be incremented nor

cleared. Its output is used to generate

Di’s and Ti’s control signals.



TR is a temporary register. The CPU uses

this register to store intermediate results

of operations. It is not accessible by the

external programs. It is loaded,

Common Bus System



The basic computer has eight registers,

a memory unit, and a control unit.



Paths must be provided to transfer

information from one register to another

and between memory and registers



A more efficient scheme for transferring

Instruction Codes

A process is controlled by a

program

 A program is a set of instructions that

specify the operations, data, and the control sequence

 An instruction is stored in binary code that

specifies a sequence of microoperations

 Instruction codes together with data are

1. Memory

2. Program Counter

The basic computer instructions are stored in the memory

The size of each memory word is 16 bits.

Each instruction occupy one word. _{0101010101010101}

1010101010101010 1100110011001100 0011001100110011 0101010101010011 1010101010101010 1100110011001100 0011001100110011 000000000001 PC

3. Instruction Register

0101010101010101 IR

Building A Basic Computer!

Instruction code format



Instruction code format with two parts : Op.

Code + Address

 Op. Code : specify 16 possible operations(4

bits)

 Address : specify the address of an

operand(12 bits)

 If an operation in an instruction code does

not need an operand from memory, the rest of the bits in the instruction (address field) can be used for other purpose

Op. Code Address

15 12 11 0

instruction

data

15 12 11 0

Instruction Cycle



A computer goes through the following

instruction cycle repeatedly:

1. Fetch an instruction from memory

2. Decode the instruction

3. Read the effective address from

memory if the instruction has an indirect

address