Microcontrollers and Applications

Microcontroller & Applications

By Mr. Asim Sayed

microprocessor and microcontroller

Microprocessors vs Microcontrollers

The contrast between a microcontroller and a microprocessor is best exemplified by the fact that most microprocessors have many operational codes (opcodes) for moving data from external memory to the CPU; microcontrollers may have one, or two.

Microprocessors may have one or two types of bit-handling instructions; microcontrollers will have many.

The microprocessor is concerned with rapid movement of code and data from external addresses to the chip; the microcontroller is concerned with rapid movement of bits within the chip.

The microcontroller can function as a computer with the addition of no external digital parts; the microprocessor must have many additional parts to be operational.

Eight-Bit Microcontrollers

Eight bits has proven to be a very useful word size for small computing tasks.

Capable of 256 decimal values or quarter-percent resolution. the 1-byte word is adequate for many control and monitoring applications. Serial ASCII data is also stored in byte sizes, making 8 bits the natural choice for data communications.

Most integrated circuit memories and many logic functions are arranged in an 8-bit configuration that interfaces easily to data buses of 8 bits.

Harvard architecture The Harvard architecture is a computer architecture with physically

separate storage and signal pathways for instructions and data.

The term originated from the Harvard Mark I relay-based computer, which stored instructions on punched tape (24 bits wide) and data in electro-mechanical counters.

These early machines had limited data storage, entirely contained within the central processing unit, and provided no access to the instruction storage as data.

Programs needed to be loaded by an operator, the processor could not boot itself.

Modified Harvard architecture

Today, most processors implement such separate signal pathways for performance reasons but actually implement a Modified Harvard architecture, so they can support tasks like loading a program from disk storage as data and then executing it.

Von Neumann architecture

This is also known as Princeton architecture.

The data and code memories are combined into one architecture.

In this architecture instruction fetching and data operations ant occur at the same time.

The design is simpler than Harvard architecture.

Microcontrollers for embedded systems

Microprocessors and microcontrollers are widely used in embedded system products.

An embedded product uses a microprocessor (or microcontroller) to do one task and one task only.

Ex. of embedded applications-

Use of microcontroller based systems and PCs.

One of the most critical needs of an embedded system is to decrease power consumption and space.

This can be achieved by integrating more functions into the CPU chip.

All the embedded processors based on the x86 and 680x0 have low

Power consumption in addition to some forms of 110, COM p011, and ROM all on a single chip.

In high-performance embedded processors, the trend is to integrate more and more functions on the CPU chip and let the designer decide which features he/she wants to use.

Criteria for choosing a microcontroller

Three criteria in choosing microcontrollers are as follows:

(I) meeting the computing needs or the task at hand efficiently and cost effectively,

(2) availability of software development tools such as compilers, assemblers, and debuggers

(3) wide availability and reliable sources of the microcontroller.

Bitwise Data Transmission

Data transmission requires:

Encoding bits as energy

Transmitting energy through medium

Decoding energy back into bits

Energy can be electric current, radio, infrared, light, smell, etc.

Transmitter and receiver must agree on encoding scheme and transmission timing

Asynchronous Transmission

One definition of asynchronous: transmitter and receiver do not explicitly coordinate each data transmission

Transmitter can wait arbitrarily long between transmissions

Used, for example, when transmitter such as a keyboard may not always have data ready to send

Asynchronous may also mean no explicit information about where data bits begin and end

E.g. when we send individual ASCII characters

Using Electric Current to Send Bits

Simple idea - use varying voltages to represent 1s and 0s

One common encoding use negative voltage for 1 and

positive voltage for 0

In following figure, transmitter puts positive voltage on line

for 0 and negative voltage on line for 1

Transmission Timing Problems

Encoding scheme leaves several questions unanswered:

How long will voltage last for each bit?

How soon will next bit start?

How will the transmitter and receiver agree on timing? Later : Self-clocking codes (e.g. Manchester Encoding)

Standards specify operation of communication systems

Devices from different vendors that adhere to the standard can interoperate

Example organizations: International Telecommunications Union (ITU)

Electronic Industries Association (EIA)

Institute for Electrical and Electronics Engineers (IEEE)

RS-232

Standard for transfer of characters across copper wire

Produced by EIA

Full name is RS-232-C

RS-232 defines serial, asynchronous communication Serial - bits are encoded and transmitted one at a time (as opposed to parallel

transmission)

Asynchronous - characters can be sent at any time and bits are not individually synchronized

Details of RS-232

Components of standard:

Connection must be less than 50 feet

Data represented by voltages between +15v and -15v

25-pin connector, with specific signals such as data, ground and control

assigned to designated pins

Specifies transmission of characters between, e.g., a terminal and a modem

Transmitter never leaves wire at 0v; when idle, transmitter puts negative

voltage (a 1) on the wire

Identifying asynchronous

characters Transmitter indicates start of next character by

transmitting a one

Receiver can detect transition as start of character

Extra one called the start bit

Transmitter must leave wire idle so receiver can detect transition marking beginning of next character

Transmitter sends a zero after each character

Extra zero call the stop bit

Thus, character represented by 7 data bits requires transmission of 9 bits across the wire

Start, Stop Bits

Typically one of the data bits might be a parity bit

(7N1, 8E1)

Timing

Transmitter and receiver must agree on timing of each bit

Agreement accomplished by choosing transmission rate

Measured in bits per second

Detection of start bit indicates to receiver when subsequent bits will arrive

Hardware can usually be configured to select matching bit rates

Switch settings

Software

Autodetection

Transmission Rates

Baud rate measures number of signal changes per second

Bits per second measures number of bits transmitted per second

In RS-232, each signal change represents one bit, so baud rate and bits per second are equal

If each signal change represents more than one bit, bits per second may be greater than baud rate

This is the case with modems nowadays!

More on this when we look at modulation

Framing

Start and stop bits represent framing of each character

If transmitter and reciver are using different speeds, stop bit will not be received at the expected time

Problem is called a framing error

RS-232 devices may send an intentional framing error called a BREAK

Duplex Two endpoints may send data simultaneously -

full-duplex communication

Requires an electrical path in each direction

If only one endpoint may send data half-duplexcommunications or simplex

Pin 2 - Receive (RxD)

Pin 3 - Transmit (TxD)

Pin 4 - Ready to send (RTS)

Pin 5 - Clear to send (CTS)

Pin 7 - Ground

Limitations on Transmission

Limitations on wires makes waveforms look like:

Longer wire, external interference may make signal look even worse

RS-232 standard specifies how precise a waveform the transmitter must generate, and how tolerant the receiver must be of imprecise waveform

Channel Capacity

Data rate In bits per second

Rate at which data can be communicated

Bandwidth In cycles per second, or Hertz

Amount of bandwidth constrained by transmitter and medium (and the feds!)

For digital data: Want as high a data rate as possible given some slice of bandwidth! Limited by the error rate

Nyquist Bandwidth(1)

If the rate of signal transmission is 2B then a signal with frequencies no greater than B is sufficient to carry the signal rate

Converse: Given a bandwidth of B, the highest signal rate that can be carried is 2B

Ex: Given 3000Hz (typical on phone lines), the capacity C of the channel is : C=2B = 6000bps

Nyquist Bandwidth(2)

Wait! But given about 3000Hz our modems go much faster than 6000bps. How?

The previous capacity assumes a binary signal element. If a signal element can represent more than one bit, the formulation becomes:

C=2B(log2M) ; M = # of signal elements

If M=32, we get C=30,000bps

Shannons Capacity

Shannons capacity includes the concept of error rates. At a given noise level, the higher the data rate, the higher the error rate. This is a theoretical maximum!

Signal to Noise Ratio: SNR = SignalPower/NoisePower

Ratio measured at the receiver

SNRdb = 10log10(SNR)

SNR of 100 = 20 dB

SNR of 1000 = 30 dB

Capacity: C = B*log2(1+SNR)

Shannon Capacity Examples

If voice telephone has a SNR of 30 dB and bandwidth of 3000 Hz: C = 3000 log2(1 + 1000) = 30,000 bps

If our LAN technology has a SNR=251, B = 1Mhz C=106*log2(252) = 8Mbps

Using Nyquists formula, the number of symbols we would need to transmit this data per signaling element:

8*106 = 2*106*log2M M = 24 = 16

RS-232 Signals

Architecturally RS-232 is a

bi-directional point to point

link.(serial port - PC side)

Two independent channels are

established for two-way (full-

duplex) communications.

RS-232 can also carry

additional signals used for flow

control (RTS, CTS) and modem

control (DCD, DTR, DSR, RI).

RS-232 Signals

Common 25 pin D-shell connector pinout used for

asynchronous data communications.

Pin Signal1 PGND Protective Ground2 TXD Transmit Data3 RXD Receive Data4 RTS Ready To Send5 CTS Clear To Send6 DSR Data Set Ready7 SG Signal Ground8 CD Carrier Detect20 DTR Data Terminal Ready22 RI Ring Indicator

(serial port - PC side)

RS-232 Line Driver Unbalanced Line Drivers

Each signal appears on the interface connector as a voltage with reference to a signal ground.

The idle state (MARK) has the signal level negative with respect to common whereas the active state (SPACE) has the signal level positive respest to the same reference.

RS-232 Speed How fast can RS-232 be?

The maximum speed, according to the standard, is 20kbit/s.

However, modern equipment can operate much faster than this.

(i.e. Lynx can reach 115200 baud.)

The length of the cable also plays a part in

maximum speed.

The longer the cable and the slower the speed at which you can

obtain accurate results.

A large wire capacitance and inductance limits the maximum

length of the cable and/or the maximum speed; Moreover higher

is the capacitance of the cable higer is the interference between

two adjacent signal wire.

50 feet (15m) @ max baudrate is commonly quoted as the

maximum distance.

It is not specified in EIA standard but its recommended respect

these values.

RS-232 sw settings

One byte of async data has:

Start Bit = 1 (always)

Data Bits = 8 (or 7)

Stop bits = 1 (or 2)

Parity = NONE (or EVEN or ODD)

+ 25

- 25

What is RS-485

What is RS-485?

RS-485 is a EIA standard interface which is very common in the data acquisition world

RS-485 provides balanced transmission line which also can be shared in Multidrop mode.

It allows high data rates communications over long distances in real world environments.

How fast can RS-485 be?

RS-485 was designed for greater distance and higher baudrates

than RS-232.

According to the standard, 100kbit/s is the maximum speed and

distance up to 4000 feet (1200 meters) can be achieved.

RS-485 Line Driver Balanced Line Drivers

Voltage produced by the driver appears across a pair of signal wires that transmit only one signal. Both wires are driven opposite.

RS-485 driver has always the Enable direction control signal.

Differential system provides noise immunity, because much of the common mode signal can be rejected by the receiver. So ground shifts and induced noise signals can be nullified.

RS-485 Network

RS-485 provides Half-Duplex, Multidrop communications over a

single twisted pair cable.

MASTER SLAVE-1

SLAVE-2 SLAVE-3

The standard specifies

up to 32 drivers and

32 receivers can share

a multidrop network

Terminator resistors

avoid reflected signal

RS-485 Half-duplex

Datalogic uses Half-Duplex configurations for Data Collecting

and Master/Slave layouts.

Usually we talk about Multidrop

network (i.e. MX4000,DPS9000)Slave 1

TX

ENABLE

RX

Slave 2

TX

ENABLE

RX

Slave N

TX

ENABLE

RX

RTX485+

RTX485-

485GND

Master

TX

ENABLE

RX

RS-485 Full-duplex Potentially RS-485 interface can also use 4-wires to comunicate in

multidrop mode but...

Scanner

TX

ENABLE

RX

TX485+

TX485-

RX485+

RX485-

485GND

TX

ENABLE

RX

Other device

RS-232 vs RS-485

The architectural difference between RS-232 and RS-485 is

that 232 is a bi-directional point to point link, whereas 485 is

a single channel bus.

Electrically, each 232 signal uses a single wire with symmetric

voltages about a common ground wire. 485 uses two wires to

carry the single signal differentially.

The big difference to the software is that only one device on a

485 bus can transmit at a time, whilst there is not similar

limitation on RS232 because is a peer-to-peer link .

RS-232 vs RS-485RS-232 RS-485

Mode of Operation SINGLE-ENDED DIFFERENTIAL

Total Number of Drivers 1 DRIVER 32 DRIVERand Receivers on One Line 1 RECEIVER 32 RECEIVER

Maximum Cable Length 50 FEET 4000 FEET

Maximum Data Rate @Max length 20kb/s 100kb/s

Driver Output Signal Level(Loaded Min.) Loaded +/-5V to +/-15V +/-1.5V

Driver Output Signal Level(Unloaded Max) Unloaded +/-25V +/-6V

Driver Load Impedance 3k to 7k 54

Max. Driver Current inHigh Z State Power On N/A N/A

Max. Driver Current inHigh Z State Power Off +/-6mA @ +/-2v +/-100uA

Slew Rate (Max.) 30V/S N/A

Receiver Input Voltage Range +/-15V -7V to +12V

Receiver Input Sensitivity +/-3V +/-200mV

Receiver Input Resistance 3k to 7k 12k

Data Format and Protocols

Information content passing through peer-to-peer connection is packed in a

very simple structure:

and are both configurable via software

(device configuration parameters)

Most common generic Handshake are available/selectable with RS232

interface:

Hardware (RTS-CTS)

Software XON/XOFF

Single ended signalling

Single-ended signaling is the simplest and most commonly used method of

transmitting electrical signals over wires. One wire carries a varying voltage

that represents the signal, while the other wire is connected to a reference

voltage, usually ground.

Single ended signaling is less expensive to implement than differential, but it

lacks the ability to reject noise caused by:

differences in ground voltage level between transmitting and receiving circuits

induction picked up on the signal wire

Ex of single ended signalling

Single-ended signaling is widely used, and can be seen in numerous common

transmission standards, including:

RS-232 serial communications

PS/2 mouse and keyboard connectors

IC serial bus

TTL circuits

CMOS logic circuits

ECL circuits

Most parallel computer buses, such as:

VMEbus

PCI

continued

Some more examples:

VGA video connectors

SCSI interfaces for hard drives and other peripherals

Parallel ATA interfaces for hard drives and other peripherals

Some kinds of connectors, though more often used for balanced pairs, are

sometimes used for single-ended operation:

RCA jacks for audio signals

TRS phone connectors for audio signals

The main advantage of single-ended over differential signaling is that fewer

wires are needed to transmit multiple signals.

If there are n signals, then there are n+1 wires - one for each signal and one

for ground. (Differential signaling uses at least 2n wires.)

A disadvantage of single-ended signaling is that the return currents for all the

signals share the same conductor (even if separate ground wires are used, the

grounds are inevitably connected together at each end), and this can

sometimes cause interference ("crosstalk") between the signals.

Differential Signalling

Differential signaling is a method of transmitting information electrically with

two complementary signals sent on two paired wires, called a differential pair.

Since external interference tends to affect both wires together, and

information is sent only by the difference between the wires, the technique

improves resistance to electromagnetic noise compared with use of only one

wire and an un-paired reference (ground).

The technique can be used for both analog signaling, as in balanced audio, and

digital signaling, as in RS-422, RS-485, Ethernet over twisted pair, PCI

Express, Display Port, HDMI, and USB. The opposite technique is called single-

ended signaling. Differential pairs are usually found on a printed circuit board,

in cables (twisted-pair cables, ribbon cables), and in connectors.

SPI

The Serial Peripheral Interface or SPI bus is a synchronous serial

data link, a de facto standard, named by Motorola, that operates in

full duplex mode.

Devices communicate in master/slave mode where the master device

initiates the data frame. Multiple slave devices are allowed with

individual slave select lines. Sometimes SPI is called a four-wire

serial bus, contrasting with three-, two-, and one-wire serial buses.

SPI is often referred to as SSI (Synchronous Serial Interface).

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The MOSI/MISO convention requires that, on devices using the alternate names, SDI on the master be connected to SDO on the slave, and vice versa.

Chip select polarity is rarely active high, although some notations (such as SS or CS instead of nSS or nCS) suggest otherwise.

Slave select is used instead of an addressing concept.

The SPI bus specifies four logic signals:SCLK : Serial Clock (output from master).MOSI : Master Output, Slave Input (output from master).MISO : Master Input, Slave Output (output from slave).SS : Slave Select (active low, output from master).

Alternative naming conventions are also widely used, and SPI port pin names for particular IC products may differ from those depicted in these illustrations:SCLK : SCK, CLK.MOSI : SIMO, SDO, DO, DOUT, SI, MTSR.MISO : SOMI, SDI, DI, DIN, SO, MRST.SS : nCS, CS, CSB, CSN, nSS, STE, SYNC.

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Serial Peripheral Interface (SPI)

SDI: data

in

SDO:

data out

SCK:

clock

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CKE configuration bit allows either falling or rising edge

of clock to be used, while CKP selects clock polarity.

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SPM bit selects whether data is sampled in middle of clock

period or at end of clock period.

Between the CKP, CKE, SPM bits there is a lot of flexibility in

how data is clocked in. Can make the SPI protocol work with

just about any serial device.

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Multiple SPI peripherals each require a separate chip select line

via parallel port line. We will concentrate on the I2C serial bus

as it does not require use of chip selects.

I2C

IC (Inter-Integrated Circuit, alternately spelled I2C or IIC, most commonly pronounced I-squared-C) is a multimaster serial single-ended computer bus invented by the Philips semiconductor division, today NXP Semiconductors, and used for attaching low-speed peripherals to a motherboard, embedded system, cellphone, or other digital electronic devices.

IC uses only two bidirectional open-drain lines, Serial Data Line (SDA) and Serial Clock Line (SCL), pulled up with resistors.

Typical voltages used are +5 V or +3.3 V although systems with other voltages are permitted.

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I2C (Inter-Integrated-Circuit) BusI2C is a two wire serial interface.

18F242

SDA

Microchip 24LC515

SDA

A2SCL

10K

10K

SCL

Vdd

Vdd

A1

A0

SDA

A2SCL

A1

A0

SCL clock line

SDA data

(bidirectional)

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What is a bus??

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I2C Features

Multiple receivers do not require separate select lines as in SPI

At start of each I2C transaction a 7-bit device address is sent

Each device listens if device address matches internal address, then device responds

SDA (data line) is bidirectional, communication is half duplex

SDA, SCLK are open-drain, require external pullups

Allows multiple bus masters (will discuss this more later).

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I2C Bus Addressing

No chip selects needed!!!!!

pullups are needed

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I2C Bus Transfer

Multiple bytes sent in a transaction; every 8 bits has a

9th bit that is an acknowledge.

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Write (master to slave)

Read (master from slave)

Master

initiates all

transactions,

read or write.

IC is appropriate for peripherals where simplicity and low manufacturing cost are more important than speed. Common applications of the IC bus are:

Reading configuration data from SPD EEPROMs on SDRAM, DDR SDRAM, DDR2 SDRAM memory sticks (DIMM) and other stacked PC boards

Supporting systems management for PCI cards, through an SMBus 2.0 connection.

Accessing NVRAM chips that keep user settings.

Accessing low speed DACs and ADCs.

Changing contrast, hue, and color balance settings in monitors (Display Data Channel).

Changing sound volume in intelligent speakers.

Controlling OLED/LCD displays, like in a cellphone.

Reading hardware monitors and diagnostic sensors, like a CPU thermostat and fan speed.

Reading real-time clocks.

Turning on and turning off the power supply of system components.

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Assembler

An assembler is a program which creates object code by translating combinations of mnemonics and syntax for operations and addressing modes into their numerical equivalents. This representation typically includes an operation code("opcode") as well as other control bits.

The assembler also calculates constant expressions and resolves symbolic names for memory locations and other entities.

The use of symbolic references is a key feature of assemblers, saving tedious calculations and manual address updates after program modifications.

Most assemblers also include macro facilities for performing textual substitutione.g., to generate common short sequences of instructions as inline, instead of called subroutines.

There are two types of assemblers based on how many passes through the source are needed to produce the executable program.

One-pass assemblers go through the source code once. Any symbol used before it is defined will require "errata" at the end of the object code (or, at least, no earlier than the point where the symbol is defined) telling the linker or the loader to "go back" and overwrite a placeholder which had been left where the as yet undefined symbol was used.

Multi-pass assemblers create a table with all symbols and their values in the first passes, then use the table in later passes to generate code.

Compiler

A compiler is a computer program (or set of programs) that transforms source code written in a programming language (the source language) into another computer language (the target language, often having a binary form known as object code).

The most common reason for wanting to transform source code is to create an executable program.

The name "compiler" is primarily used for programs that translate source code from a high-level programming language to a lower level language (e.g., assembly language or machine code).

If the compiled program can run on a computer whose CPU or operating system is different from the one on which the compiler runs, the compiler is known as a cross-compiler.

A cross compiler is necessary to compile for multiple platforms from one machine. A platform could be infeasible for a compiler to run on, such as for the microcontroller of an embedded system because those systems contain no operating system.

In paravirtualization one machine runs many operating systems, and a cross compiler could generate an executable for each of them from one main source.

Debugger

A debugger or debugging tool is a computer program that is used to test and debug other programs (the "target" program).

The code to be examined might alternatively be running on an instruction set simulator (ISS), a technique that allows great power in its ability to halt when specific conditions are encountered but which will typically be somewhat slower than executing the code directly on the appropriate (or the same) processor.

Some debuggers offer two modes of operationfull or partial simulationto limit this impact.

A "trap" occurs when the program cannot normally continue because of a programming bug or invalid data. For example, the program might have tried to use an instruction not available on the current version of the CPU or attempted to access unavailable or protected memory.

When the program "traps" or reaches a preset condition, the debugger typically shows the location in the original code if it is a source-level debugger or symbolic debugger, commonly now seen in integrated development environments.

If it is a low-level debugger or a machine-language debugger it shows the line in the disassembly (unless it also has online access to the original source code and can display the appropriate section of code from the assembly or compilation).

IDE

An integrated development environment (IDE) or interactive development environment is a software application that provides comprehensive facilities to computer programmers for software development.

An IDE normally consists of a source code editor, build automation tools and a debugger.

Most modern IDEs offer Intelligent code completion features.

Some IDEs contain a compiler, interpreter, or both, such as Net Beans and Eclipse; others do not, such as SharpDevelop and Lazarus.

The boundary between an integrated development environment and other parts of the broader software development environment is not well-defined.

Sometimes a version control system and various tools are integrated to simplify the construction of a GUI. Many modern IDEs also have a class browser, an object browser, and a class hierarchy diagram, for use in object-oriented software development.