IAS0430

MICROPROCESSOR

SYSTEMS

Fall 2018

The 2nd lecture

Martin Jaanus U02-308

martin.jaanus@ttu.ee 620 2110, 56 91 31 93

Learning environment : http://isc.ttu.ee

Materials : http://isc.ttu.ee/martin

Topics

The digital electronics in analogue world

• Logic functions ( not, nand,nor,xor.....)

• Realization of logic functions (DTL, TTL, KMOP....)

• Devices with memory (decoders,multiplexers)

• Devices with memory (triggers,counters)

Digital electronics

• Digital ( latin language digitis – finger, digit)

• A digital signal is a signal that is being used to represent

data as a sequence of discrete values; at any given time it

can only take on one of a finite number of valuesPõhiline

kasutus on kahendsüsteem , sest seda on lihtne kasutada

(signaal kas on või ei ole)

• This contrasts with an analog signal, which represents

continuous values; at any given time it represents a real

number within a continuous range of values.

• Usually in digital electronics has also time discrete values.

Binary system

• Two possible values

• The simpliest digital system . Bitt.

• 0 – False, missing, low level

• 1- True, present, high level

• Fuzzy logic is a form of many-valued logic in which the

truth values of variables may be any real number between

0 and 1. It is employed to handle the concept of partial

truth, where the truth value may range between

completely true and completely false.

The Binary system in elecronics• Current based (industrial electronis, automation)

0 - 4 mA, 1 – 20 mA , if current is missing, circuit is faulty.

In consumer electronics usually voltage based:

0 – 0...0.5 V , 1 – 2.4.....(3.3 V , 5 V)

In industial communication and electronics can be also used other levels 0 >>5 V, 1 < -5V...-24 V (RS232)

Logic states can be coded into AC voltage or current -: amplitude,frequency, phase. Modern communication technology.

Separation zone

History

• 1705 Binary system (0,1) Gottfried Wilhelm Leibniz

• 1886 Georg Boole algebra (logic gates), relay logic

• 1907 The usage of Audion (electon valve) in NAND gate.

• 1924 predecessors of modern logic gates.

• 1941 The first electonically programmable device (Konrad

Zuze, Z3), used electronic valves.

• 1953 The first fully semiconductor based computer.

• 1958 The first logic IC.

Digital control module of automation(1973)

USSR

History

• The usage of simple logic gates has decreased because

of usage microprocessors, but anyway those components

are hidden inside those devices.

• The usage of simle logic gates is required when speed is

important.

Digital control module of

automation(1982) USSR

• It is neccecarry that logic gates confirm states, positive

feedback is required:

The transfer function of inverter.

The Binary system in elecronics

Logical operation - negation

• Without this operation the digital electronics is not

possible!

• 0 1 ja 1 0 Y=X

X Y X Y

Logical operation – negation (inversion)

• The simpliest way – to use one transistor.

• Transistor must be in closed or saturated state.

TTL CMOS

The CMOS technology is the most popular, it does not consume energy in static

state.

Discrete components

Logical operation – negation (inversion)

• The problem in digital circuit– transfer to others state must

be as quick as possible !

• The solution : Decrease supply voltage (power depends of root of

voltage ) and if it is possible – working frequency.

• Cooling

Parasitic

capacitors need

to recharged !

Current

Connecting digital devices

• The programmer sees only 0 and 1

• In real circuit there are existing voltages and currents– They are always analogue values ! When you design circuits you must take it into account !

• The next gate consumes energy (CMOS switching, TTL continiously), the output must allow it .

• In usual case there is possible connect to output 10 next inputs.

High

Low

High

HighLow Low

Logical operation – OR

• The gate with at least 2 inputs.

• The output is 1 kui at least one input is 1.

• Y=X1+X2+....Xn

X1 X1

Y Y

X2 X2

Logical operation – OR

• The simpliest realization– use diodes.

• Example from consumer electonics – Device is powered

from battery OR from power network.

• Drawback – voltage drop in diode is 0.7 V

• The dicrete elements can used in simpliest application. It is

not used inside IC!

(1973)

Logical operation – AND

• The gate with at least 2 inputs.

• The output is 1 if all inputs are 1.

• Y=X1*X2*....Xn

X1 X1

Y Y

X2 X2

Logical operation – AND• The simpliest realization– use diodes..

• This operation happens when you connect open collector gates.

• Data busses (näit I2C)

• The discrete elements can used in simplest application. It is not used inside IC!

Vcc

Combined operations

To get all logic funcionality you should have

• negation (NOT) and one of these – AND or OR gate .

• If you have them, no more is physically required.

• The basic logic gates are NAND (the most popular) or

NOR gates.

1973 The Soviet Union, Texas Instruments 1966

X1 X1

Y Y

X2 X2

NAND

• One possible basic logic block

• The cascade connection of AND and NOT gates.

• The output is 1 if at least one input is 0

• Y=X1*X2*....Xn

You only need this component to make any logic circuit

(Charles Sanders Peirce proved in 1880)

• One possible basic logic block

• The cascade connection of OR and NOT gates.

• The output is 0 if any input is 1

• Y=X1+X2+....Xn

You only need this component to make any logic circuit

X1 X1

Y Y

X2 X2

NOR

Exclusive OR (XOR)

• Two inputs

• Output is 1 if the inputs are different.

• Y=X1+ X2

• Can be made using NOR or NAND gates.

• The main usage is inside microprocessor (the part of

adder)X1 X1

Y Y

X2 X2http://www.circuitstoday.com/half-adder

The half adder

Exclusive NOR (XNOR)

• Two inputs

• The output is 1 if inputs are equal.

• Y=X1+X2

• Can be made using NOR or NAND gates..

• It can be used in synchronus detector.

X1 X1

Y Y

X2 X2

The corridor switch

Gates with third state

• It is not possible to connect outputs of usual logic gates

together . It is possible to use gate with open collecor, but

then we get additional NAND operation.

• To make it possible, some gates have possibility to beak the

output (move it to high impedance mode high-Z)

• Usually this input is labeled as ENABLE

• Usage – in microprotsessor systems to connect different

devices to one bus.

Decoder

• A binary decoder is a combinational logic circuit that converts binary

information from the n coded inputs to a maximum of 2n unique

outputs. They are used in a wide variety of applications, including

data demultiplexing, seven segment displays, and memory address

decoding.

http://www.interfacebus.com/ic-bcd-to-7-segment-decoder-schematic.html

Multiplexer

• A multiplexer (or mux) is a device that selects one of

several analog or digital input signals and forwards the

selected input into a single line.

Transmission line

Multiplekser

• Has 2n inputs and n addres inputs

• Connects selected input with output.

• The input is detemineb by addres.

https://commons.wikimedia.org/wiki/File:Mux_from_3_state_buffers.png#/media/File:Mux_from_3_state_buffers.png

Demultiplexer (demux)

• One input, 2n outputs

• Connects selected output with input.

• The output is detemined by addres.

Logic devices with memory (triggers)

• Can store one bit of information.

• The information is stored until the power is on.

• Synchronous trigger ( changes states only during clock pulse)

• Asynchronous trigger (changes states immediately when input changes)

• Nonlinearity and positive feedback is required.

The idea of memory- hysteresis (1973, USSR)

RS Flip-Flop

• S - Set, R – Reset

• The simplest memory, but has forbidden state

• Asynchronous, changes states immediately when input changes.

R=S=1 is not allowed !

Synchronisation

• The logic gates work in real-time (asynchronously).

• The most of digital systems work synchronously.

• The states change only when clock signal is active (falling

or rising edge of signal or both).

CLOCK – kell

Transition time must be lower than Δt.

Clock frequency f=1/ Δt

Synchronous RS flip-flop

• Reacts only when clock signal is active, usually AND

gates are added.

• State S=1 ja R=1 is forbidden(this is allowed in JK trigger,

what is 2 RS triggrs in cascade connection+logic).

D –flip-flop (memory cell)

• D – delay –>

• iF D=1 then active front of clock switches it always to state 1.

• iF D=0 then active front of clock switches it always to state 0.

The other flip-flops

• The JK flip-flop augments the behavior of the SR flip-flop

(J=Set, K=Reset) by interpreting the J = K = 1 condition

as a "flip" or toggle command.

• If the T input is high, the T flip-flop changes state

("toggles") whenever the clock input is strobed. If the T

input is low, the flip-flop holds the previous value. (division

by 2)

• Combined flip-flops. The combination with logic gates.

• http://www.circuitstoday.com/flip-flop-conversion

Nowdays computer memory RAM

• Random Access Memory

• Static (based on flip-flops), thefastest, expencive

• Dynamic (memory cell – capacitor), takes less space, but needs refreshing – charge decreases during time.

• The information is stored until the power is on !

SRAM DRAM

https://en.wikipedia.org/wiki/Random-access_memory

Nowdays computer memory ROM

• Read Only Memory

• The infomation is stored even the power is off .

• The outer connections are similar with RAM .

The idea of ROM:https://www.cl.cam.ac.uk/teaching/1213/SysOnChip/materials/sg3bus/zhp4c6e8640b.html

• ROM – The information is entered in production

• EPROM – information can be programmed by

user ( to erase UV light is needed)

• EEPROM – Electrically erasable and

programmable memory (slow)

• Flash EEPROM , same, but faster

https://en.wikipedia.org/wiki/Flash_memory

• The drawback of EEPROM memories. There is

limited write cycles.

• The RAM memory can be replaced with flash

memory in some cases.