PIC introduction + mapping

PIC MICROCONTROLLER

By : Osama Hasan

AN INTRODUCTION TO PIC MICROCONTROLLERS

- The name PIC was originally an acronym for "Programmable Intelligent Computer".

- A PIC microcontroller is a processor with built in memory and RAM and you can use it to control your projects.

- What this really means for you is that you have a very powerful device that has many useful built in modules e.g.

* EEPROM.* Timers.* Analogue comparators.* UART.

INTRODUCTION (CONT.)

low cost ,wide availability with high clock speed

availability of low cost or free development tools

Only 37 instructions to remember serial programming and re-programming with

flash memory capability Its code is extremely efficient, allowing the PIC

to run with typically less program memory than its larger competitors

PIC is very small and easy to implement for non-complex problems and usually accompanies to the microprocessors as an interface

Why PIC is popular?

TWO DIFFERENT ARCHITECTURES

Harvard Architectures

(newer arch.) Von-Neumann

Architecture

TWO DIFFERENT ARCHITECTURES

Von-Neumann Architecture

Used in: 80X86 (CISC PCs) Only one bus between CPU

and memory RAM and program memory

share the same bus and the same memory, and so must have the same bit width.

Harvard Architectures

Used mostly in RISC CPUs

Separate program bus and data bus: can be of different widths

For example, PICs use: Data memory (RAM): a small

number of 8bit registers Program memory (ROM):

12bit, 14bit or 16bit wide (in EPROM, FLASH, or ROM)

RISC VS. CISC

Used in: 80X86, 8051, 68HC11, etc. Many instructions

(usually > 100) Several addressing modes Usually takes more than 1 internal clock cycle

(Tcyc) to execute

Complex Instruction Set Computer (CISC)

Is a computer where single instructions can execute several low-level operations (such as a load from memory, an arithmetic operation, and a memory store) and/or are capable of multi-step operations or addressing modes within single instructions.

RISC VS. CISC

Used in: SPARC, ALPHA, Atmel AVR, etc. Few instructions (usually < 50) Only a few addressing modes Executes 1 instruction in 1 internal clock cycle

(Tcyc)

Reduced Instruction Set Computer (RISC)

Is a CPU design strategy based on the insight that simplified instructions can provide higher performance if this simplicity enables much faster execution of each instruction. A computer based on this strategy is a reduced instruction set computer also called RISC.

FAMILY CORE ARCHITECTURE DIFFERENCES

The PIC Family: Cores

12bit cores with 33 instructions: 12C50x, 16C5x

14bit cores with 35 instructions: 12C67x,16Cxxx

16bit cores with 58 instructions: 17C4x,17C7xx

‘Enhanced’ 16bit cores with 77 instructions: 18Cxxx

THE PIC FAMILY: SPEED

Can use crystals, clock oscillators, or even an RC circuit. Some PICs have a built in 4MHz RC clock, Not very

accurate, but requires no external components! Instruction speed = 1/4 clock speed (Tcyc = 4 * Tclk) All PICs can be run from DC to their maximum specified

speed:4MHz 12C50x

10MHz 12C67x

20MHz 16Cxxx

33MHz 17C4x / 17C7xxx

40MHz 18Cxxx

CLOCK AND INSTRUCTION CYCLES Instruction Clock

Clock from the oscillator enters a microcontroller via OSC1 pin where internal circuit of a microcontroller divides the clock into four even clocks Q1, Q2, Q3, and Q4 which do not overlap.

These four clocks make up one instruction cycle (also called machine cycle) during which one instruction is executed.

Execution of instruction starts by calling an instruction that is next in string.

Instruction is called from program memory on every Q1 and is written in instruction register on Q4.

Decoding and execution of instruction are done between the next Q1 and Q4 cycles. On the following diagram we can see the relationship between instruction cycle and clock of the oscillator (OSC1) as well as that of internal clocks Q1-Q4.

Program counter (PC) holds information about the address of the next instruction.

CLOCK AND INSTRUCTION CYCLES (CONT.)

PIPELINING IN PIC

THE PIC FAMILY: PROGRAM MEMORY

Technology: EPROM, FLASH, or ROM It varies in size from one chip to another.

- examples:

12bit instructions

512 12C508

14bit instructions

1024( 1k) 16C711

14bit instructions

8192( 8k) 16F877

16bit instructions

16384( 16k) 17C766

MICROCHIP PIC 16F84 MICROCONTROLLER

High Performance RISC CPU:

Only 35 single word instructions to learn

All single cycle instructions except for program branches, which are two-cycle

Operating speed: DC - 20 MHz clock input DC - 200 ns instruction cycle


Below is a diagram showing the pin-outs of the PIC 16F84. We will go through each pin, explaining what each is used for.


RA0 To RA4RA is a bidirectional port. That is, it can be configured as an input or an output. The number following RA is the bit number (0 to 4). So, we have one 5-bit directional port where each bit can be configured as Input or Output.RB0 To RB7RB is a second bidirectional port. It behaves in exactly the same way as RA, except there are 8 - bits involved.


VSS And VDDThese are the power supply pins. VDD is the positive supply, and VSS is the negative supply, or 0V. The maximum supply voltage that you can use is 6V, and the minimum is 2V.

OSC1/CLK IN And OSC2/CLKOUTThese pins is where we connect an external clock, so that the microcontroller has some kind of timing.


MCLRThis pin is used to erase the memory locations inside the PIC (i.e. when we want to re-program it. In normal use it is connected to the positive supply rail.

T0CK1This is another clock input, which operates an internal timer. It operates in isolation to the main clock.


Below is a diagram showing the pin-outs of the PIC 16F84. We will go through each pin, explaining what each is used for.

PORT A

PORT B

PIC DATA MEMORY

The data memory is devided into 4 memory banks

The most important registers have addresses in all the four banks

THE REGISTERS

A register is a place inside the PIC that can be written to, read from or both.

you will notice is that it is split into two - Bank 0 and Bank 1. Bank 1 is used to control the actual operation of the PIC, for example to tell the PIC which bits of Port A are input and which are output. Bank 0 is used to manipulate the data.

An example is as follows: Let us say we want to make one bit on Port A high. First we need to go to Bank 1 to set the particular bit, or pin, on Port A as an output. We then come back to Bank 0 and send a logic 1 (bit 1) to that pin.

THE REGISTERS

The most common registers in Bank 1 we are going to use are STATUS, TRISA and TRISB. The first allows us to come back to Bank 0, TRISA allows us to select which pins on Port A are output and which are input, TRISB allows us to select which pins on Port B are output and which are input. The SELECT register in Bank 0 allows us to switch to Bank 1.

STATUS To change from Bank 0 to Bank 1 we tell the STAUS register. We do this by setting bit 5 of the STATUS register to 1. To switch back to Bank 0, we set bit 5 of the STATUS register to 0. The STATUS register is located at address 03h.

THE REGISTERS

TRISA and TRISB.

These are located at addresses 85h and 86h respectively. To program a pin to be an output or an input, we simply send a 0 or a 1 to the relevant bit in the register.

So, on Port A we have 5 pins, and hence 5 bits. If I wanted to set one of the pins to input, I send a ‘1’ to the relevant bit. If I wanted to set one of the pins to an output, I set the relevant bit to ‘0’. The bits are arranges in exactly the same way as the pins, in other words bit 0 is RA0, bit 1 is RA1, bit 2 is RA2 and so on.

RA0 RA1 RA2 RA3 RA4 PORT A Pin

0 1 2 3 4 Bit Number

0 1 1 0 0 Binary

THE REGISTERS

W ( working register )

The W register is a general register in which you can put any value that you wish. Once you have assigned a value to W, you can add it to another value, or move it. If you assign another value to W, its contents are overwritten.

THE REGISTERS

Now what he have to do is turn an LED on. We do this by making one of the pins (the one with the LED connected to it) high. In other words, we send a ‘1’ to the pin. movlw 02h movwf 05h

movlw 00h movwf 05h

So, now our LED is on, we now need to turn it off:

REGISTER ADDRESSING MODES

Direct Addressing:Uses 7 bits of 14 bit instruction to identify a register file address 8th and 9th bit comes from RP0 and RP1 bits of STATUS register.

PIC PERIPHERALS

The PIC microcontroller has many built in peripherals and this can make using them quite daunting at first which is why I have made this introductory page with a summary of each major peripheral block.

PIC PERIPHERALS

PIC microcontrollerFeature

PIC microcontroller feature description

Flash memory Re-programmable program storage.

RAM Memory storage for variables.

EEPROM Long term stable memory : Electrically

Erasable Programmable Read

Only Memory.

I/O ports High current Input/output ports

(with pin direction change).

USART Built in RS232 protocol (only needs level translator chip).

PIC PERIPHERALS

Flash memoryThis is the program storage area and gives you the most important benefit for using a PIC microcontroller - You program the device many times.

PIC microcontroller RAMThe PIC microcontroller RAM size is also important as it stores all your variables and intermediate data.

Note: You can usually alter the program to use less RAM by choosing the right variable sizes or changing how your program works

For example don't use floating point alter it to use a different variable type e.g. you can use long integers with fixed point operation to avoid floating point.

PIC PERIPHERALS

PIC microcontroller EEROM

Electrically Erasable ROM is used to store data that must be saved between power up and power down.

This area is readable and writable and has a much longer life than the main program store i.e. it has been designed for more frequent use.

PIC PERIPHERALS

I/O PortsInput / Output ports let you communicate with the outside world so you can control leds, LCDs or just about anything with the right interface. You can also set them as inputs to gather information.

Pin directionMost PIC microcontroller pins can be set as an input or and output and this can be done on the fly e.g. for a dallas 1 wire system a pin can be written to generate data and read at a later stage. The TRIS register controls the I/O direction and setting a bit in this register to zero sets the pin as output while setting it as one sets the pin as input.

Thanks for Attendance

PIC introduction + mapping

Technology

Transcript of PIC introduction + mapping