EET 203 MICROCONTROLLER SYSTEMS DESIGN LECTURE 1 INTRODUCTION

EET 203 MICROCONTROLLER SYSTEMS DESIGN LECTURE 1: INTRODUCTION TO MICROCONTROLLER

WHAT IS MICROCONTROLLER? The microcontroller is simply a computer on a chip Essential for the operation of devices such as mobile phones, DVD players, video cameras, and most self-contained electronic systems Working sometimes with other chips, but often on its own The MCU provides the key element in the vast range of small, programmed devices which are now commonplace

BASIC MICROCONTROLLER SYSTEM Element of Digital System Basic microcontroller system contains 3 elements Processor Handle (Central Processing Unit) data operations Make calculations

BASIC MICROCONTROLLER SYSTEM Memory To store program and data Two types Input and Output To communicate with outside world (other devices) Two types of communication Volatile loses its data when switched off, but can be written by the CPU to store current data RAM (Random Access Memory) Non-Volatile retains its data when switched off ROM (Read Only Memory) Serial Data is transmitted 1 bits at 1 time Parallel The data is usually transferred in and out more than 1 bits at a time (8 or 16 bits Controller has all these in one single chip

PIC 16 F 877 A MICROCONTROLLER MCU Features Things that need to be considered before selecting the right microcontroller for application Program Executions Overview of how the program being executed by the microcontroller RAM File registers Observe all the registers available in microcontroller

MCU FEATURES Some main features to consider are Numbers of inputs and outputs Program memory sizes Data RAM sizes 256 x 8 bits EEPROM Maximum clock speed 368 x 8 bits RAM Non-volatile data memory 8 k (8096 x 14 bits) of Flash ROM program memory 20 MHz Range of interfaces Development system support Cost and availability

MCU FEATURES Numbers of inputs and outputs 5 ports with total 32 I/O pins Port A – 5 pins Port B – 8 pins Port C – 8 pins Port D – 8 pins Port E – 3 pins Can operate as 1 pin or combine as 1 port Each pins has multiple functions

PROGRAM EXECUTIONS This chip has to be programmed via the serial programming pins, PGM, PGC and PGD The fixed-length instructions (contains both the operation code and operand) are being written to FLASH ROM

RAM FILE REGISTERS Contains 368 x 8 bits file register Divided into 4 blocks (known as register bank) Including Special Function Register (SFR) Have dedicated function Located at low address at every register bank General Used Purpose Register (GPR) to store variable created in C program (Start at address 0020 H)

RAM FILE REGISTERS

RAM FILE REGISTERS

MCU CONFIGURATIONS Operational modes (cip configuration words)must be set prior to the main program download Clock oscillator types Watchdog timers Power up reset Brown-out reset Low voltage programming Code protection In-circuit debug modes

CIP CONFIGURATION WORD the assembler directive __CONFIG is included at the top of the program, which sets up aspects of the chip operation which cannot be subsequently changed without reprogramming The function of each bit is shown in Table 1. 2, along with some typical configuration settings. Details can be found in the data sheet

CIP CONFIGURATION WORD

CIP CONFIGURATION WORD IN-CIRCUIT DEBUGGING (ICD) the program to be downloaded after the chip has been fitted in the application circuit, and allows it to be tested with the real hardware With ICD, the chip can be programmed, and reprogrammed during debugging, while avoiding possible electrical and mechanical damage caused by removal from the circuit. The normal debugging techniques of single stepping, breakpoints and tracing can be applied in ICD mode. This allows a final stage of debugging in the prototype hardware, where problems with the interaction of the MCU with the real hardware can be resolved.

CIP CONFIGURATION WORD LOW VOLTAGE PROGRAMMING When the chip is programmed, a high voltage (12– 14 V) is applied to the PGM pin (RB 3) To avoid the need to supply this voltage during in-circuit programming (e. g. during remote reprogramming), a low-voltage programming mode is available; Using this option means that RB 3 is not then available for general I/O functions during normal operation

CIP CONFIGURATION WORD POWER-UP TIMER When the supply power is applied to the programmed MCU, the start of program execution should be delayed until the power supply and clock are stable, otherwise the program may not run correctly. The power-up timer may therefore be enabled (PWRTE 0) as a matter of routine. It avoids the need to reset the MCU manually at start up, or connect an external reset circuit, as is necessary with some microprocessors. An internal oscillator provides a delay between the power coming on and an internal MCU reset of about 72 ms. This is followed by an oscillator start up delay of 1024 cycles of the clock before program execution starts. At a clock frequency of 4 MHz, this works out to 256 μs.

CIP CONFIGURATION WORD BROWN-OUT RESET Brown out refers to a short dip in the power-supply voltage, caused by mains supply fluctuation, or some other supply fault, which might disrupt the program execution If the Brown-Out Detect Enable bit (BODEN) is set, a PSU glitch of longer than about 100 μs will cause the device to be held in reset until the supply recovers, and then wait for the power-up timer to time out, before restarting. The program must be designed to recover automatically. rown out refers to a short dip in the power-supply

CIP CONFIGURATION WORD WATCHDOG TIMER The watchdog timer is designed to automatically reset the MCU if the program malfunctions, by stopping or getting stuck in loop. This could be caused by an undetected bug in the program, an unplanned sequence of inputs or supply fault. A separate internal oscillator and counter automatically generates a reset about every 18 ms, unless this is disabled in the configuration word. If the watchdog timer is enabled, it should be regularly reset by an instruction in the program loop (CLRWDT) to prevent the reset. If the program hangs, and the watchdog timer reset instruction not executed, the MCU will restart, and (possibly) continue correctly, depending on the nature of the fault.

CIP CONFIGURATION WORD RC OSCILLATOR The MCU clock drives the program along, providing the timing signals for program execution. The RC (resistor–capacitor) clock is cheap and cheerful, requiring only these two inexpensive external components, operating with the internal clock driver circuit, to generate the clock. The time constant (product R C) determines the clock period. A variable resistor can be used to give a manually adjustable frequency, although it is not very stable or accurate.

CIP CONFIGURATION WORD CRYSTAL OSCILLATOR If greater precision is required, especially if the program uses the hardware timers to make accurate measurements or generate precise output signals, a crystal (XTAL) oscillator is needed. Normally, it is connected across the clock pins with a pair of small capacitors (15 p. F) to stabilise the frequency. The crystal acts as a self-contained resonant circuit, where the quartz or ceramic crystal vibrates at a precise frequency when subject to electrical stimulation. The oscillator runs at a set frequency with a typical accuracy of better than 50 parts per million (ppm), which is equivalent to /− 0. 005%. A convenient value (used in our examples later) is 4 MHz; this gives an instruction cycle time of 1 μs, making timing calculations a little easier (each instruction takes four clock cycles). This is also the maximum frequency allowed for the XT configuration setting. The PIC 16 FXXX series MCUs generally run at a maximum clock rate of 20 MHz, using a high-speed (HS) crystal which requires the selection of the HS configuration option.

CIP CONFIGURATION WORD CONFIGURATION SETTINGS The default setting for the configuration bits is 3 FFF, which means that the code protection is off, in-circuit debugging disabled, program write enabled, low-voltage programming enabled, brown-out reset enabled, power-up timer disabled, watchdog timer enabled and RC oscillator selected. A typical setting for basic development work would enable in-circuit debugging, enable the power-up timer for reliable starting, disable the watchdog timer and use the XT oscillator type. By default, the watchdog timer is enabled. This produces an automatic reset at regular intervals, which will disrupt normal program operation. Therefore, this option will usually be disabled (bit 2 0). Conversely, it is generally desirable to enable the power-up timer, to minimise the possibility of a faulty start-up