Presentation is loading. Please wait.

Presentation is loading. Please wait.

- 1 - Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Microcontrollers.

Similar presentations


Presentation on theme: "- 1 - Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Microcontrollers."— Presentation transcript:

1 - 1 - Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Microcontrollers Interfaces & Orcad Marco Benocci, PhD

2 - 2 - Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Signal processing: math library. Real-time nature: latency, scheduling. Portability: lifetimey constraint (specially when battery-driven). Microcontrollers Interfaces Embedded specialized processor targeted for a specific application Photo: o Signal re-sampling o Signal generation: Periodic: Cosinusoidal, Sinusoidal, Square, Rectangular, Saw tooth, Dirac seq. Non-periodic: Noise, Ramp, Step, Dirac. o Operators : Multiplication, Division, Sine, Cosine, Arc sine, Arc cosine, Absolute, Square root, Natural logarithm, Binary logarithm or base 2 logarithm, Common logarithm or base 10 logarithm, Exponential, Power, Random o Windowing : Bartlett, Blackman, Hamming, Gauss, Hann, Kaiser, Welch o Vectors: Power, Minimum, Maximum, Negate, Zero padding, Copy, Partial Convolution, Convolution o Filtering: FIR, least mean square, interpolation, IIR o Transforms (Complex Fast Fourier Transform, Complex inverse Fast Fourier Transform, Real to complex Fast Fourier Transform) o IMA/DVI ADPCM

3 - 3 - Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Microprocessor (Central Processing Unit, CPU) First design in late-1960s. MP944 implemented the F-14A Central Air Data Computer. Intel 4004 in General purpose (i.e. Intel Core, PowerPC). Features: ALU + sequencer + register (no memory or peripherals). Three basic tasks: perform mathematical operations, move data between memory locations and follow sets of instructions. The job of starting up the computer specifically involves the bootstrap loader. The assembler translates semantic instructions developed by designers into a language the CPU can use. Microcontroller (MCU) The microcontroller is the integration of a number of useful functions into a single IC package specialized form of microprocessor designed to be self- sufficient and cost-effective. Texas Instruments TMS1802 single-chip (4-bit) calculator device was designed in Features: processor + data/program memory + digital IO. Application areas: automobiles, office machines, toys, and appliances. Digital Processor: general VS special purpose

4 - 4 - Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Focus on MCU Performance Metrics: Low Power consumptions: Harvester needs less than 1uW i.e. Atmel PicoPower (165μA/MHz). Cheap Price: consumer products. i.e. MC9S08QG4 costs less than 1$ featuring 4 KB FLASH, 256 B RAM. n.b. the package influences the final price due to the soldering. Easiness of integration: number and kind of Interfaces i.e. STM32 (ARM Cortex M-3) provides USB Host, I2C, SPI, Ethernet, SDIO, CAN. High computational power: MIPS (Million of Instructions Per Seconds) i.e. ARM Cortex A-8: 2, GHz. CORTEX ARM Cortex family is a complete processor core that provides a standard CPU and system architecture. Three main profiles: A profile for high end applications, R for real time and M for cost-sensitive and microcontroller applications. The Cortex-M3 provides a standardised microcontroller core which goes beyond the CPU to provide the entire heart of a microcontroller (including the interrupt system, SysTick timer, debug system and memory map).

5 - 5 - Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Interfaces: policies Visions Real-time behavior Efficient, economical i.e. centralized power supply Bandwidth and communication delay Inverse relation between volume and urgency Electrical robustness Single-ended vs. differential signals Fault tolerance Error detecting & error correcting bus protocols Maintainability Diagnosability Security & Safety Error detecting and error correcting bus protocols Privacy Encryption, virtually private Transfert Modalities FIFO Buffer: temporarily store acquired data Interrupts: the slowest but most common method DMA (Direct Memory Access): is a system whereby samples are automatically stored in system memory while the processor does something else

6 - 6 - Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Interfaces: signal acquisition Analog Analog To Digital Converter (ADC) Digital To Analog Converter (DAC) … Digital Subsistem Control Low speed serial interfaces Programmable Timers GPIO Real time clock Watchdog Timer Host Interface Connectivity USB PCI IEEE (Ethernet) IEEE a/b7g (WiFi) IEEE (WPAN) IEEE 1394 (Firewire) Asynchronous Memory Flash Storage Card Storage Asynch Memory ATAPI/Serial ATA Flash Storage Card SDRAM/DDR Data Streaming Low Speed Serial Interfaces USB 2.0 Full Speed (12Mbps) 10BaseT Ethernet IEEE b Synch Serial Audio/Data Ports Host Interface IEEE a/g 100BaseT Ehternet USB 2.0 High Speed (480Mbps) IEEE 1394 (Firewire) Parallel Video/Data Ports Gigabit Ethernet PCI/ PCI Express Signal Conditioning Sensors and Actuator IEEE1451 input/data acquisition, signal processing, output/display Data acquisition system components:

7 - 7 - Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 The IEEE 1451 standard defines the architecture that achieve to the sensors, instruments and systems to work together with relative ease. The IEEE 1451 vision underlines the change of the computer role: the intelligence is distributed over the network. The innovative concept of Smart sensor aims to: move intelligence closer to the point of measurement/control; create confluence of transducers, computation and communication towards common goal; make sensor cost effective to integrate/maintain distributed systems. IEEE 1451 A TIM contains: from 1 to 255 transducers (can be a mix of sensors and actuators); signal conditioning and processing electronics; address logic (or microprocessor) to implement a standardized Transducer Interface (wired or wireless) defined by IEEE 1451.X (.2,.3,.5,.6, ) between the TIM and NCAP; a TEDS. A NCAP integrates: a neutral smart transducer object and data models that allow NCAP to communicate sensor data and information to any network; NCAP to NCAP communications (defined by IEEE ); application programming interfaces (API) and a common set to access transducers from a network (defined by IEEE ).

8 - 8 - Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Smart sensors is a transducer or an actuator easy to install, maintain, modify and upgrade. Integration of extensible Transducer Electronic Data Sheet (TEDS): a memory area inside the sensor where sensor identification information, calibration data, measurement range are stored. Simplify the data exchange over the network (standard engineering units). Self-identification, self-diagnostic. Time aware for time stamping and correlation: Triggering and control model defines how channels are accessed. IEEE : Smart Sensor

9 - 9 - Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 The physics of their operation. One physical principle can be used to measure many different phenomena. e.g. piezoelectric effect can measure force, flexure, acceleration, heat, and acoustic vibrations. The particular phenomenon they measure. One phenomenon can be measured by many physical principles. e.g. sound waves can be measured by the piezoelectric effect, capacitance, electromagnetic field effects, and changes in resistance. By a particular application. e.g. one could group all sensors together that can be used to measure distance. Active VS passive. Passive: the physical phenomena observed modifies some electrical characteristics of the sensor that can be observed supply external power (e.g. RFID). Self-generating sensor: the power is absorbed by the observed physical phenomena and transform in electric power in output (e.g. RFID & Sensing). Energy. Middelhoeks classification energy domain such as electrical, thermanl, radiation, nechanical, magnetic, (bio)- chemical. Technology. e.g. MEMS Sensors: Classification

10 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna FS Sensors: Calibration Alma Mater Studiorum Facoltà di Ingegneria, Bologna FSO (Full Scale Output) Upper – Lower [endpoint of output] Calibration Relationship between sensor output e applied physical input Error Measured value – true value [% of FSO] Offset Sensor output for zero applied input Hysteresis Max [value approached with decreasing input - value approached with increasing input] Sensitivity Max deviation of calibration point from straight line [% of FSO] Accuracy Max deviation of calibration point from straight line [% of FSO] Repeatability Max deviation of calibration point from straight line [% of FSO] Resolution Smallest change in the physical variable that results in a detectable change in the sensor output Frequency response Change with frequency of out/in magnitude ratio and phase difference for sinusoidally varying input Cross-sensitivity Sensitivity of sensor of a variable than the physical quantity under measurement Stability Ability of sensor to reproduce output for identical input and condition over time Vout Saturation Bias Non Linearity Mechanical Misalignements (Factory) Bias Drift

11 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Sensors: Signals continuous-time, continuous-valued (real) discrete-time, continuous-valued (sampled) continuous-time, discrete-valued (quantified) discrete-time, discrete-valued (numeric) Sampled Real Quantified Numeric Time interval definition (t0, t0+t) Nature (Time interval definition [t0, t0+t]) Features Peak value (plus): Peak value (minus): Peak-Peak: Mean: RMS: Signal Nature to Voltage Convertion Current to Voltage Resistance to Voltage Signal Energy to Voltage Capacitance to Voltage "Conditioning" of a signal basically means to manipulate a signal in such a way that it meets the requirements of the next stage for further processing. translate the sensors output to a selected voltage modifying the sensors dynamic range to maximize the accuracy of the data acquisition system removing unwanted signals limiting the sensor's spectrum

12 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Conditioning the FSR Resistance to Voltage Thresholding Hardware Interrupt generation If the sensor's voltage is greater than the threshold, the output of the circuit is maximum (typically 5V). If the sensor's output is less than the threshold, the output of the circuit is minimum (usually 0V). FSR Force sensing resistors use the electrical property of resistance to measure the force (or pressure) applied to a sensor. FSR – Force Sensor Resistor Inseguitore (Av=1)

13 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 ADC The analog and continuous time signals measured by the sensor and modified by the signal conditioning circuitry must converted into the form a computer can understand. Aliasing Impossible to reconstruct fast signals after slow sampling: multiple fast signals share same sampled sequence (mind Harry Nyquist) Example: Signal: 5.6 Hz; Sampling: 9 Hz Equivalent circuit for the sample and hold Sample and hold circuitry The ADC must have a stable signal in order to accurately perform a conversion: the sample and hold circuitry take a snapshot of the sensor signal and hold the value. The switch connects the capacitor to the signal conditioning circuit once every sample period. The capacitor then holds the voltage value measured until a new sample is acquired.

14 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/ ADC Architectures There are many different ADC architectures: Successive Approximation (SAR); Sigma Delta (SD or ); Slope or Dual Slope; Pipeline; Flash...as in quick, not memory.

15 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 ADC in MSP430 (SAR 12bit) Key idea: binary search Set MSB='1 (if too large: reset MSB) Set MSB-1='1(if too large: reset MSB-1) e.g. successive approximation t V V in V-V- V-V- e.g. quantization noise for sine wave N = (approximated - real signal) called quantization noise. Features: resolution (i.e. 12bit) maximum conversion rate (i.e. 200 ksps) sampling periods controller (i.e. software or timers) on-chip reference voltage generation (i.e. 1.5 V or 2.5 V) individually configurable external input channels single-channel, repeat-single-channel, sequence, and repeat-sequence conversion modes number of storage registers cross-talking Resolution12bit Quantum Vin

16 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 DAC PWM signals are often used to create analog signals in embedded applications. We create a sine wave level with pulse-width modulated (PWM) signals from Timer_B

17 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 UART (universal asynchronous receiver / transmitter), Goldon Bell 1971 (?) Asynchronous. UART controller is the key component of the serial communications subsystem of a computer. The UART takes bytes of data and transmits the individual bits in a sequential fashion. 7- or 8-bit data with odd, even, or non-parity LSB-first data transmit and receive Simple compatibility with RS232 The start bit is always a 0 (logic low), which is also called a space. Cheap: serial transmission of digital information (bits) through a single wire or other medium is much more cost.f Standard baudrate: 2400, 19200, 57600,115200, … Focus: reliability The UART usually does not directly generate or receive the external signals used between different items of equipment. Typically, separate interface devices are used to convert the logic level signals of the UART to and from the external signaling levels. than parallel transmission through multiple wires. UART CTSClear to Send This line indicates that the Modem is ready to exchange data. DCDData Carrier Detect When the modem detects a "Carrier" from the modem at the other end of the phone line, this Line becomes active. DSRData Set Ready This tells the UART that the modem is ready to establish a link. DTRData Terminal Ready This is the opposite to DSR. This tells the Modem that the UART is ready to link. RTSRequest To Send This line informs the Modem that the UART is ready to exchange data. RIRing Indicator Goes active when modem detects a ringing signal from the PSTN.

18 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Pros Asynchronous serial devices, such as UARTs, do not share a common clock. Compatible with RS232C Cons Each device has its own, local clock. The devices must operate at exactly the same frequency (baudrate automatical detection). Logic (within the UART) is required to detect the phase of the transmitted data and phase lock the receivers clock to this. UART RS232C An old standard (1960), originally intended for connecting computer equipment (computers or terminals, referred to as DTE) to communication equipment (DCE). RS232C is are commonly used in conjunction with UART because they share the same protocol. RS232 Voltages are V for a logic 0, and -5V..-25V for a logic 1 (Reverse polarity) DB-25

19 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 I2C I2C (inter-integrated circuit), Philips1982 Philips Semiconductor I2C specification v2.1 (http://www.nxp.com/acrobat_download2/literature/9398/ pdf)http://www.nxp.com/acrobat_download2/literature/9398/ pdf) IC (Inter Communication Bus) fabrication process (NMOS, CMOS, bipolar) Half-duplex, synchronous, multi-master bus Two wires: serial data (SDA), serial clock (SCL) Each device is recognized by a unique address and can operate as either a transmitter or receiver. A master is the device which initiates a data transfer on the bus and generates the clock signals to permit that transfer. At that time, any device addressed is considered a slave. Standard-mode, up to 400 kbit/s in the Fast-mode, or up to 3.4 Mbit/s in the High-speed mode. 10-bit extended addressing for new designs (7-bit addresses all exhausted). Focus: minimizes interconnections eliminates the need for address decoders and other glue logic the multi-master capability allows rapid testing of end-user equipment via external connections simple design/upgrade Clones: present restriction of timing and voltage levels, introduction of interrupt signal Intel SMBus (System Management Bus): speed 10 a 100 kHz Intel PMBus: speed < 400 kHz DECT cordless phone base-station.

20 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 A. Enable I2C Act as the Master Enable I2C Mode 7 bit addressing DMA I2C Pros multimaster no chip select or arbitration logic required transmission control Clock stretching – when the slave (receiver) needs more time to process a bit, it can pull SCL low. The master waits until the slave has released SCL before sending the next bit. General call broadcast – addresses every device on the bus Cons The number of interfaces connected to the bus is solely dependent on the bus capacitance limit of 400 pF. Limited to about 10 feet for moderate speeds. Need external hardware: lines pulled high via resistors, pulled down via open-drain drivers (wired-AND) Half-duplex

21 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 SPI (Serial Peripheral Interface Bus), found on Motorola's M68HC11 family of CPUs in 2001 Data is simultaneously transmitted and received. Master/slave relationship. Interprocessor communications in a multiple-master system. 3-pin and 4-pin SPI operation 7- or 8-bit data length 2 data signals: MOSI – master data output, slave data input MISO – master data input, slave data output 2 control signals: SCLK – clock /SS – slave select (no addressing) The serial clock line [SCK] synchronizes shifting and sampling of the information on the two serial data lines. The master places the information onto the MOSI line a half-cycle before the clock edge that the slave device uses to latch the data. Four possible timing relationships can be chosen by using the Clock Polarity [CPOL] and Clock Phase [CPHA] bits in the Serial Peripheral Control Register [SPCR]. Data rates as high as 1 Mbit per second are accommodated when the system is configured as a master; rates as high as 2 Mbits per second are accommodated when the system is operated as a slave. SPI

22 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Pros Full duplex communication Higher throughput than I²C or SMBus Flexibility for the bits transferred (arbitrary choice of message size, content, and purpose) Simple hardware interfacing o Typically lower power requirements than I²C or SMBus due to less circuitry (including pullups) o Slaves use the master's clock, and don't need precision oscillators o Slaves don't need a unique address -- unlike I²C or GPIB or SCSI o Signals are unidirectional allowing for easy Galvanic isolation Cons Requires more pins on IC packages than I²C No in-band addressing; out-of-band chip select signals are required on shared buses No hardware flow control No hardware slave acknowledgment Supports only one master device Only handles short distances compared to RS-232, RS-485, or CAN-bus SPI

23 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 SPI vs. I 2 C For point-to-point, SPI is simple and efficient Less overhead than I 2 C due to lack of addressing, plus SPI is full duplex. For multiple slaves, each slave needs separate slave select signal More effort and more hardware than I 2 C SPI I2CI2C SPI Simultaneus transfert As the register transmits the byte to the slave on the MOSI signal line, the slave transfers the contents of its shift register back to the master on the MISO signal line, exchanging the contents of the two shift registers.

24 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 PWM (Pulse-Width Modulated): communication throw a width-capture of a precise external pulse i.e. drive servo-motors PWM Alma Mater Studiorum Facoltà di Ingegneria, Bologna

25 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Interface a digital smart sensor LIS302DL o 3-axis digital accelerometer o Range: - ±2g or ±8g o Output Interface: I2C or SPI (CMOS) o Max Data rate (ODR): 400Hz o Bandwidth: ODR/2 o Turn-on Time: 3/ODR o Sensitivity: 18 or 72 mg/LSB No external conditioning circuit need for C/V convertion and voltage translation Internal 8 bit ADC Serial Bridge Advantages provided by Smart sensors (ctrl flags, interrupts, energy duty-cycling,...) Capacitive Sensor

26 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Interface a digital sensor: SPI 1.Init (RW=0; AD5:0=0x20; D7:0=0x47) Enable X, Y, Z axis – DR=400; FS = ±2g | n.b. CTRL_REG 2 does not need deafult value change 2.Read X Low Data (RW=1; AD5:0=0x29) Read D7:0 value Register Memory Mapping Serial Bridge Control Registers SPI Communication Management Enable Filter for Free-Fall Wake Up

27 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Fieldbus (or field bus) is the name of a family of industrial computer network protocols used for real-time distributed control, now standardized as IEC A complex automated industrial system such as a manufacturing assembly line usually needs an organized hierarchy of controller systems to function. In this hierarchy there is usually a Human Machine Interface (HMI) at the top, where an operator can monitor or operate the system. This is typically linked to a middle layer of programmable logic controllers (PLC) via a non-time- critical communications system (e.g. Ethernet). At the bottom of the control chain is the fieldbus which links the PLCs to the components which actually do the work such as sensors, actuators, electric motors, console lights, switches, valves and contactors (Wiki). Relevant examples: CAN: Controller Area Network Profibus: Process Field Bus TTP: Time-Triggered-Protocol FlexRay: designed to be faster and more reliable than CAN and TTP MAP: bus designed for car factories IEEE 488: designed for laboratory equipment EIB: European Installation Bus Field Busses

28 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011

29 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 ORCAD/Cadence Capture contains extensive parts libraries that may be used to generate schematics that stand alone or that interact with PSpice, or Layout, or both simultaneously. The pins on a Capture part can be mapped into the pins of a PSpice model and/or the pins of a physical package in Layout. PSpice is a CAE tool that contains the mathematical models for performing simulations, and Layout is a CAD tool that converts a symbolic schematic diagram into a physical representation of the design. Netlists are used to interconnect parts within a design and connect each of the parts with its model and footprint. In addition to being a CAD tool, Layout also functions as a front-end CAM tool by generating the data on which other CAM. Computer-Aided Engineering (CAE) tools cover all aspects of engineering design from drawings to analysis to manufacturing. Computer-aided design (CAD) is a category of CAE that is related to the physical layout and drawing development of a system design. Electronic design automation (EDA) reduce development time and cost because they allow designs to be simulated and analyzed prior to purchasing and manufacturing hardware.

30 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Printed Circuit Board (PCB) A PCB consists of two basic parts: a substrate (the board) printed wires (the copper traces). The substrate provides a structure that physically holds the circuit components and printed wires in place and provides electrical insulation between conductive parts. A common type of substrate is FR4, which is a fi berglass–epoxy laminate. Substrates are also made from Tefl on, ceramics, and special polymers. During manufacturing the PCB starts out as a copper clad substrate as shown in Fig A rigid substrate is a C-stage laminate (fully cured epoxy). The copper cladding may be copper that is plated onto the substrate or copper foil that is glued to the substrate. A substrate can have copper on one or both sides. Multilayer boards are made up of one or more single- or double-sided substrates called cores. A core is a copper-plated epoxy laminate. The cores are glued together with one or more sheets of a partially cured epoxy. PCB

31 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Layout is used to design the PCB by generating a digital description of the board layers for photoplotters and CNC machines, which are used to manufacture the boards. There are separate layers for : routing copper traces on the top, bottom, and all inner layers; drill hole sizes and locations; soldermasks; silk screens; solder paste; part placement; board dimensions. PCB Design Process: OrCAD Layout

32 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Layout format files (.MAX) Layout uses.MAX extension while you are designing your board. Gerber Files When you are ready to fabricate your board, Layout postprocesses the design and converts it into a format that the photoplotters and CNC machines can use (Gerber files). A separate Gerber file is created for each of the layers (distinguible by the extension). Assembly layers These files are used for automated assembly of a finished board. Solder-paste layer. It is used to make a contact mask for selectively applying solder paste onto the PCBs pads so that components can be reflow soldered to the board. There may be a solder-paste layer for the top side of the board (.SPT) and one for the bottom side (.SPB). Assembly layer, which contains information for automatic component placement machines (pick-and-place machines) as to the part type, its position, and its orientation on the board. As with the soldermask, there may be an assembly layer for the top side of the board (.AST) and one for the bottom side (.ASB). OrCAD Layout: File format

33 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Basic procedure for generating a schematic in Capture and converting the schematic to a board design in Layout: 1.Start Capture and set up a PCB project using the PC Board wizard. 2.Make a circuit schematic using OrCAD Capture. 3.Use Capture to generate a Layout netlist and save it as a.MNL file for Layout. 4.Start Layout and select a PCB technology template (.TCH file). 5.Save the Layout project as a.MAX project file. 6.Use Layout to import the.MNL netlist into the.MAX file. 7.Make a board outline. 8.Position the parts within the board outline. 9.Autoroute the board. 10.Run the postprocessor to generate fi les used to manufacture the PCB. Overview of the Design Flow

34 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Industry Standards How big and what shape should the board outline be? Where should the parts be placed and in what order? What kind of layer stackup should be used? How wide and far apart should the traces be routed? What grounding and shielding techniques should be used? Is there a right way to do it, and who says so? There are several standards related to PCB design to solve these questions. The organizations below set standards that may be guides, rules for certification, or even laws: Institute for Printed Circuits (IPC-Association Connecting Electronics Industries) Electronic Industries Alliance (EIA) Joint Electron Device Engineering Council (JEDEC) International Engineering Consortium (IEC) Military Standards American National Standards Institute (ANSI) Institute of Electrical and Electronics Engineers (IEEE)

35 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Performance classes PCBs can fall into any of three end-use performance classes. Class 1, General Electronic Products, includes general consumer products (televisions, electronic games, and personal computers) that are not expected to have extended service lives and are not likely to be subjected to extensive test or repairability requirements. Class 2, Dedicated-Service Electronic Products, includes commercial and military products that have specifi c functions such as communications, instrumentation, and sensor systems, from which high performance is expected over a longer period of time. Since these items usually have a higher cost they are usually repairable and must meet stricter testing requirements. Class 3, High-Reliability Electronic Products, includes commercial and military equipment that has to be highly reliable under a wide range of environmental conditions. Examples include critical medical equipment and weapons systems. They typically have more stringent test specifi cations and possess greater environmental robustness and reworkability. Producibility levels The three producibility levels are: Level A, general designpreferred complexity Level B, moderate designstandard complexity Level C, high designreduced producibility complexity PCB Issues

36 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Minimum recommended spacing

37 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Ground Issues Typical signal and return connection schemes. Left) parallel connected Right) Series connected Signal and return connection parallel and series schemes in Layout

38 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Solve routing problems If the signal path is relatively close to the return path, the return signal will automatically flow through the GND plane directly below the signal trace (in DC circuits, current follows the path of least resistance). AC currents will follow the path of least impedance and, particularly on PCBs, the path of least inductance In a typical PCB the power distribution system contains one or more power and ground planes. The power and ground planes are like very wide traces (have little inductance) and are usually adjacent to each other (high capacitance). Ok for the power distribution system Problem occurs in high-speed digital systems when gates switch from one state to another: switching noise. Common ground plane

39 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Switching Noise Because the power and ground planes are not superconductors there is a drop in voltage between the supply pins of the gate and where power is connected to the PCB (same for the return plane). Remember that there is always some amount of resistance and inductance even on the so-called ground plane. Rail collapse: the drop in the positive rail Ground bounce: the rise in ground potential. The primary purpose of bypass capacitors in digital circuits is to promote a stable PCB power distribution system and prevent rail collapse and ground bounce. The bypass capacitors act as lowpass fi ters and short out power supply transients (noise) before they get to the amplifliers. the supply voltages across the PCB while the gate is switching

40 Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Split power and ground planes The solution to the problem of digital noise being injected into analog circuitry through the supply planes is to segregate the analog components from the digital ones and eliminate common return paths. Segregating the components is straightforward; the components are physically placed in different places on the board. a)Continuous plane b) Split plane c) Moated plane d)Isolated, coutinuous plane


Download ppt "- 1 - Universität Dortmund Alma Mater Studiorum Facoltà di Ingegneria, Bologna Marco Benocci, PhD – Microcontroller Interfaces – MPHS 2010/2011 Microcontrollers."

Similar presentations


Ads by Google