Writing about pic-18 in computer desing subject - Essay Example

? Essay: PIC 18 Microcontrollers [School] Number] June 3, Contents Introduction 3 History 3 Development4 1.Base Line PIC 4 2.Mid-Range PIC 4 3.Enhanced Mid-Range PIC 4 4.PIC 18 5 Memory Variation for PIC 18 5 PIC 18 Harvard Architecture 6 Pipelining 8 Performance 9 Features and Peripherals of PIC 18 10 I/O Ports 11 Memory 11 Conclusion 13 Works Cited 15 Introduction A microcontroller is an in-built computer chip that is used for performing specific tasks such as displaying information through LEDs or any other remote controlled devices. The most popular set of microcontrollers are those in the 8051 family. These 8051 family is a preferred choice for professionals specializing in embedded systems because they are cheap, readily available, have a larger user base and also the ability of being reprogrammed with flash memory. Figure 1: The 8051 Microcontroller Invention of the Intel 8051 led to a revolutionary role of microcontrollers in the embedded systems industry. Intensive research in this field led to design of efficient, high performance and low power consumption family of microcontrollers. These included AVR, PIC and ARM. These modern microcontrollers are every day being made smarter to include latest communication protocols like USB, I2C, SPI, Ethernet and CAN. History The name PIC refers to the Peripheral Interface Controller. The first PIC was developed in 1975 by the Microelectronics Division of a company known as General Instruments. It was developed when the Microelectronics Division was testing its 16-bit CPU i.e. CP 1600. The PIC controller was used to improve the overall performance of the CP1600 by offloading the I/O tasks. After the General Instruments converted their Microelectronics Division to Microchip Technology in 1985, they launched an 8-bit PIC 16C84 which could be programmed using the serial method in 1993. Then later in 1998, the improved version of PIC 16C84 i.e. PIC 18F84 and PIC 18F84A with a flash memory was launched. Development Figure 2: PIC microcontrollers Microchip Technology continued to improve on the then available microcontrollers, adding new complex architectures based on the Harvard architectures. Based on the architecture, the 8-bit PIC microcontroller is divided into four categories including the PIC 18. 1. Base Line PIC They are the least complex family of the 8-bit PIC microcontroller since they are based on 12-bit instruction architecture. They are the smallest and the cheapest of all the PICs and are available 6 to 40 pin packaging. 2. Mid-Range PIC These are based on 14-bit instruction architecture with a 20 MHz clock speed. They are mostly used for industry and even hobbyists because of their availability in many peripherals like Op-Amps, ADC, PWM and other communication protocols like SPI, I2C and SPI. 3. Enhanced Mid-Range PIC These are an enhanced version of Mid-Range core. They provide a greater performance in terms of flash memory, clock speed and power consumption. They also include multiples peripherals and protocols like SPI, I2C and USART. 4. PIC 18 It is the highest performing among the 8-bit PIC families and is based on a 16-bit instruction architecture that incorporates an advanced RISC architecture. It is integrated with current communication protocols like TCP/IP protocol, LIN, CAN and USB for communication with internet based networks. Figure 3: PIC 18 Pin Out Memory Variation for PIC 18 PIC 18 is available with many memory options such as mask ROM, EPROM and flash memory. These different types of memories are denoted as follows; Symbol Memory Type Example C EPROM PIC16Cxxx CR Mask ROM PIC16CRxxx F Flash Memory PIC16Fxxx The operating voltage of the PIC 18 ranges from 2.0-5.5 volts. The letter ‘L’ is included in the controllers name to denote their voltage range i.e. PIC16LFxxx (operating at 2.0-5.5 range) PIC18 Architecture PIC18 microcontrollers are based the Reduced Instruction Set Computing architecture (RISC). This is the kind of architecture where the hardware gets reduced with an increase in system speed. PIC18 microcontrollers are based on the Harvard architecture for the transfer of data internally. In this kind of architecture, there are two separate memories for program and data. These separate memories are accessed through different buses for data communication between memory and CPU. A discussion that arises is if PIC 18 are 8-bit microcontrollers, then why are they being based on an 16-bit instruction set? PIC 18 being an 8-bit microcontroller means its CPU can transmit and receive a maximum of 8-bits of data at a time. Also the statement that PIC 18 is based on 16-bit instruction means that the assembly instruction sets are 16-bit. The figure below shows an 8-bit bus and a program memory interfaced with 16-bit bus. Figure 4:8-bit bus interfaced with 16-bit bus. PIC 18 Harvard Architecture PIC 18 contains an 8-bit Arithmetic Logic Unit (ALU) and an 8-bit Accumulator (Working Register). It also contains General Purpose Registers (GPRs) and Special Function Registers (SFRs). Combination of all these performs 8-bit arithmetic and logic functions that normally require two operands. One of the operands is stored in the in the WREG (accumulator) while the other one is stored in GPR/SFR. The ALU and WREG store that two data that is processed. The diagram below shows a simple machine cycle in PIC 18 Microcontroller which consists of 4 oscillation periods. This implies that an instruction will require 4 clock periods for it to be executed. Figure 5: A simple machine cycle in PIC 18 Microcontroller This PIC 18 architecture has its own advantages and disadvantages. The advantages include; It employs the RISC architecture that helps increases its speed of operation The instruction set is small and easy to learn Supports a wide range of interfaces including SPI, USART, PWN and Ethernet Easy availability of processors in DIL package makes them easy to handle hence more professionals are interested However this architecture also comes with its drawbacks. These include; Accommodates only one accumulator For access to the entire RAM of many devices, register –bank switching will be required There is no orthogonal relationship between the operations and the registers hence some instructions can address RAM and or immediate constants while others only utilizes the accumulator Pipelining Processor controllers that existed before PIC 18 had the ability to fetch or execute a single instruction within a unit time. However the current microcontrollers like PIC 18 have a higher instruction throughput because of their ability to fetch and execute instruction in the same time. This is referred as to instruction pipelining which involves processing of instructions into different steps for better performance as shown below. Figure 6: Pipelining Performance The PIC 18 Harvard architecture was aimed at optimization of the speed to cost ratio. This architecture was amongst the first architectures in CPU design but it still remains the cheapest and simplest. This architecture simplifies the design and the design greatly. This simplicity becomes important in other areas like price, clock speed and power consumption. The PIC 18 was implemented to be applied on fast look up tables. These look ups can only be complete using a single instruction taking two instruction cycles. This is the basic model of any basic function. This kind of optimization is made possible by a relatively large program space on the PIC. Construction of a real-time code is made simplifier by the scalar nature of the PIC. This makes it easier to calculate the execute time by simply multiplying the line count of the listing of the PIC assembler by the instruction cycle time. This kind of method is not possible in other CPUs. Therefore precise timing is very critical in developing low-level applications. Real time features of the PIC can be a great deal in saving crucial engineering design. For a PIC 18, the interrupt latency is three instruction cycles and this is a unique but yet still useful property of the PICs. This constant is unaffected even if the instructions take either one or two cycles. Therefore external interrupts has to be synchronized with the four clock instruction cycle. This constant value for latent enables the PICs to achieve interrupt driven low jitter timing sequences. For other microcontrollers, the interrupt has to be anticipated by the non-interrupt code but for PICs, but for PIC 18 this is not necessary. Sometimes the three-cycle latency is increased because the PIC normally fails to store its registers when it is set to enter interrupt time. Only four instructions are required to store both the status register, W-register and the switch to some specific bank before the actual interrupt processing is restarted. Features and Peripherals of PIC 18 PIC 18 microcontrollers consists of the following features; Has a C compiler with an optimized architecture that has an extended instructional set Has a 100,000 erase/write cycle with an enhanced flash Has typical program memory Consist of a flexible oscillator option with; A four crystal mode that includes a high-precision PLL or USB A total of two external clock modes that have speeds up to 48MHZ An internal oscillator that has 8 user selectable frequencies ranging from 31KHz to 8MHz A dual oscillator options that allows the microcontroller and USB module to run at different clock speeds The PIC 18 consists of the following peripherals; I/O Ports PIC 18 has five input-output ports i.e. PORTA, PORTB, PORTC, PORTD and PORTE which are 8-bit. Both port B and port D have 8 I/O pins unlike the other three ports. The diagram below shows a schematic presentation of the I/O ports. Figure 7: I/O ports for PIC 18 Memory PIC 18 consists of three different sections of memories i.e. Flash memory: This is a non-volatile memory i.e. retains data even if power is cut off, that is used data downloaded by a user in to the microcontroller. EEPROM: This refers to a non-volatile memory that is used to store data values in certain defined variables. SRAM: This refers to the Static Random Access Memory and is very volatile. This means it loose data as soon as power is cut off. An 8x8 Multiplier: This is a hardware that performs multiplications in a single machine cycle hence providing a higher computational throughput and reduction in operation cycle and length of the code. Oscillator: PIC 18 has very flexible clock options i.e. an external clock of up to 48MHz is applied. It consists of an internal oscillator that provides frequency options varying from 31 KHz- 8 MHz Counters: It has four times and one is an 8-bit timer while the rest selects between 8 and 16 modes. Counters are very useful in calculating the precise time between two operations. ADC Interface: PIC 18 has thirteen analog to digital converter channels of a resolution of 10-bits. An ADC reads an analog input and converts it into a form i.e. digital that can be understood by the microcontroller. Interrupts: PIC 18 has three external interrupt sources and twenty internal associated with other peripherals like USART, Timers and ADC EUSART: These refer to the Enhanced Universal Synchronous and Asynchronous Serial Receiver and Transmitter module. This is a full-duplex asynchronous system but can also be configured as a half-duplex system. It has several features like automatic wake upon sync break reception and automatic baud rate calibration. These features make it suitable for use in a Local Interconnect bus system. SPI: PIC 18 works well with a 3-wire SPI communication on common clock source between two devices. ICSP and ICD: The serial controllers of PIC 18 have an In Circuit Serial Programming facility that programs the memory. However they can be programmed without removal of the IC form the circuit. In the circuit debugger, the ICD allows the debugging of the hardware while the controller is still in the circuit. I2C: Its supports a Two Wire Interface hence can work as a master and slave device between two devices. USB: Under different clock options it has the ability to support full speed USB. PIC 18 microcontrollers are very popular among many professionals in the embedded systems industry. They are not only popular because of they are cheap or readily available, but also because of the programming aspect. Microchip technology provides free IDE package which includes a simulator, debugger and an assembler. They also commercially sell C compilers for developers to use in their development. Other development tools are open source. PICs find many uses in almost all current electronic and computing devices ranging from computers to smartphones and many other digital electronics. Most of these devices are required to perform complex functions and hence a PC will require proper programming in order to enable them carry put their functions appropriately. That is why Microchip technology has provided free IDEs, APIs and making other development tools open source to enable more people participate the development of these embedded systems that are crucial in the device they run. Most of electrical appliances that require some processing contain a PIC to enable them carry out their functions. Electrical and Computer engineering involves the study of the design and the functionality of these electronic and computing devices. Since most of these devices have microcontrollers that help them perform their duties, therefore the study of PICs in Electrical and Computer engineering becomes very essential. Conclusion A microcontroller is an in-built computer chip that is used for performing specific tasks such as displaying information through LEDs or any other remote controlled devices. The 8051 family was the preferred choice of microcontroller for professionals specializing in embedded systems. This is because they were cheap, readily available, had a larger user base and the ability of being reprogrammed with flash memory. However, modern microcontrollers are every day being made smarter to include latest communication protocols like USB, I2C, SPI, Ethernet and CAN. Therefore PIC 18 was an improvement of earlier versions of microcontrollers to include new complex architectures based on the Harvard architectures for the transfer of data internally. PIC18 is the highest performing among the 8-bit PIC families and is based on a 16-bit instruction architecture that incorporates an advanced RISC architecture. It is integrated with current communication protocols like TCP/IP protocol, LIN, CAN and USB for communication with internet based networks. It operates on a voltage range of 2.0-5.5 volts. It also has a higher instruction throughput because of its ability to fetch and execute instruction in the same time i.e. instruction pipelining PIC 18 finds many applications in Electrical and Computer Engineering because of its subtle features. This will include; a C compiler with an optimized architecture, 100,000 erase/write cycle with an enhanced flash and a typical program memory. It also consists of various peripherals like I/O ports, memory, oscillator, counters, ADC interface and USB. Works Cited Mazidi, Muhammad A., Rolin D. McKinlsy, and Danny Causey. Pic Microcontroller And Embedded Systems: Using Assembly and C for Pic18. New York: Publisher Pearson Education, Limited, 2008. Print. "PIC Microcontroller Tutorial : Introduction, Basics & Architecture - EngineersGarage." EngineersGarage | Inspiring Creations. N.p., n.d. Web. 29 Apr. 2013. "8051 Microcontroller Tutorial | Atmel 8051 Architecture - EngineersGarage." EngineersGarage | Inspiring Creations. N.p., n.d. Web. 29 Apr. 2013. Read More