I came across a very nice article at tinkerlog.com explaining why you need to use a current limiting resistor to power your leds. They say:
In this post I will try to show, why it’s a good idea to use a current limiting resistor for an LED. And when it’s safe to drive the LED without any resistor.

If you read about LEDs, you will notice that everyone tells you, that you need a current limiting resistor. But mostly they do not tell you why.

For more information visit here.

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Jal is a high-level language for a number of Microchip (TM) PIC microcontrollers (16c84, 16f84, 12c508, 12c509, 16F877) and Ubicom SX (SX18 and SX28) microcontrollers. It was created by Wouter van Ooijen. He created Jal because he did not like any of the low-cost (or free) languages for these chips and implementing a high level language looked like a nice project. Implementing an existing HLL seemed more difficult and less fun than creating his own, so he just started writing the compiler and the language evolved on with it. Sorry for all C-lovers, but Jal is more like Pascal. For a quick impression of Jal you could read either the summary or the examples section of the on-line manual.

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Lecture series on Embedded Systems by Dr.Santanu Chaudhury,Dept. of Electrical Engineering, IIT Delhi .

Lecture 1 -Embedded Systems: Introduction

Lecture 2 -Embedded Hardware

Lecture 3 -PIC: Instruction Set

Lecture 4 -PIC Peripherals On Chip

Lecture 5 -ARM Processor

Lecture 6 -More ARM Instructions

Lecture 7 -ARM: Interrupt Processing

Lecture 8 -Digital Signal Processors

Lecture 9 -Discrete Fourier Transform (DFT)

Lecture 10 -DFT (Contd.)

Lecture 11 -DFT (Contd.) Introduction to Z Transform

Lecture 12 -Z Transform

Lecture 13 -Virtual Memory and Memory Management Unit

Lecture 14 -Bus Structure

Lecture 15 -Bus Structure 2

Lecture 16 -Bus Structure 3 (Serial Interfaces)

Lecture 17 -Serial Interfaces

Lecture 18 – Power Aware Architecture

Lecture 19 -Software for Embedded Systems

Lecture 20 -Fundamentals of Embedded Operating Systems

Lecture 21 -Scheduling Policies

Lecture 22 -Role of Models in Production Management

Lecture 23 -Financial Evaluation of capital Decisions

Lecture 24 -Networked Embedded System

Lecture 25 -Networked Embedded Systems – II

Lecture 26 -Network Embedded System III

Lecture 27 -Network Embedded System IV

Lecture 28 -Designing Embedded Systems

Lecture 29 -Designing Embedded Systems – II

Lecture 30 -Designing Embedded Systems- III

Lecture 31 -Embedded System Design – IV

Lecture 32 -Designing Embedded Systems – V

Lecture 33 -Platform Based Design

Lecture 34 -Compilers for Embedded Systems

Lecture 35 -Developing Embedded Systems

Lecture 36 -Embedded Systems

Lecture 37 -The Fieldbus Network – I

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PIC16F84A için hazırlanmış kod şeması aşağıdaki gibidir. Bu şema sayesinde kendi kodlarınızı daha rahat oluşturabilirsiniz.

;****************************************************
;   This file is a basic code template for assembly code generation   *
;   on the PICmicro PIC16F84A. This file contains the basic code      *
;   building blocks to build upon.                                    *
;                                                                     *
;   If interrupts are not used all code presented between the ORG     *
;   0x004 directive and the label main can be removed. In addition    *
;   the variable assignments for 'w_temp' and 'status_temp' can       *
;   be removed.                                                       *
;                                                                     *
;   Refer to the MPASM User's Guide for additional information on     *
;   features of the assembler (Document DS33014).                     *
;                                                                     *
;   Refer to the respective PICmicro data sheet for additional        *
;   information on the instruction set.                               *
;                                                                     *
;   Template file assembled with MPLAB V4.00.00 and MPASM V2.20.12.   *
;                                                                     *
;*******************************************************
;                                                                     *
;    Filename:        xxx.asm                                           *
;    Date:                                                            *
;    File Version:                                                    *
;                                                                     *
;    Author:                                                          *
;    Company:                                                         *
;                                                                     *
;                                                                     *
;****************************************************
;                                                                     *
;    Files required:                                                  *
;                                                                     *
;                                                                     *
;                                                                     *
;****************************************************
;                                                                     *
;    Notes:                                                           *
;                                                                     *
;                                                                     *
;                                                                     *
;                                                                     *
;***************************************************

list      p=16F84A            ; list directive to define processor
#include <p16F84A.inc>        ; processor specific variable definitions

__CONFIG   _CP_OFF & _WDT_ON & _PWRTE_ON & _RC_OSC

; '__CONFIG' directive is used to embed configuration data within .asm file.
; The lables following the directive are located in the respective .inc file.
; See respective data sheet for additional information on configuration word.

;***** VARIABLE DEFINITIONS
w_temp        EQU     0x0C        ; variable used for context saving
status_temp   EQU     0x0D        ; variable used for context saving

;*****************************************************
ORG     0x000             ; processor reset vector
goto    main              ; go to beginning of program

ORG     0x004             ; interrupt vector location
movwf   w_temp            ; save off current W register contents
movf    STATUS,w          ; move status register into W register
movwf    status_temp       ; save off contents of STATUS register

; isr code can go here or be located as a call subroutine elsewhere

movf    status_temp,w     ; retrieve copy of STATUS register
movwf    STATUS            ; restore pre-isr STATUS register contents
swapf   w_temp,f
swapf   w_temp,w          ; restore pre-isr W register contents
retfie                    ; return from interrupt

main

; remaining code goes here

END                     ; directive 'end of program'

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En çok tercih edilen PIC çeşitlerinden biri olan PIC16F84A için 35 adet assembly anahtar kodu bulunmaktadır. Bu komutların tamamını ve ne işe yaradıklarını aşağıdaki resimleri inceleyerek anlayabilirsiniz. İlk resim anlatılacak komutların bir özetini gösteriyor.  Diğer resimler teker teker kodların ne işe yaradıklarını anlatıyor. Kolay gelsin.

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Mentor Graphics
These days embedded developers are looking for new and cost-efficient methods to maximize the performance of their application while still maintaining a high level of design efficiency. This paper takes a look at three proven methodologies for improved performance through simple code modifications. The three areas explored include: measuring worst case and average case interrupt latency, measuring loading, and reducing program size while increasing run time performance.

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Programı buradan indirebilirsiniz. Microbrn klasörü içinde microbrn.exe dosyasına tıklayarak proramı çalıştırın. Program açıldığında soldaki resimdeki gibi bir pencere açılacaktır. İlk iş olarak File\Port yolunu izleyerek K128 pic programlayıcınızın hangi portta bulunduğunu programa anlatın. USB Port isimlerini ezbere bilmiyorsanız, Device Manager (Aygıt Yöneticisi ) ‘ne girerek aygıtın hangi portta bağlı bulunduğunu öğrenebilirsiniz. Bu ayarı yaptıktan sonra program penceresi aşağıdaki şekildeki gibi olmalıdır. 

Program tanıtımı

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Bu program DIY Electronics tarafından geliştirilen DIY K128 programlama kartı için üretilen yazılımdır. Derleyerek HEX uzantısına çevirdiğimiz programları PIC  içeresine atmaya yarar. Piyasada pic programlayıcı adıyla satılan ürünlerin çoğu K128 pic proglama kartıdır. Bu kartı üreten kişi elinde hangi kutu varsa onun içine koyar o yüzden kutusu her renk olabilir. K128 programlama kartının devre şemasına buradan ulaşabilirsiniz. K128 için hazırlanan ingilizce kullanma kulavuzuna buradan ulaşabilirsiniz.Aşağıda bendeki DIY K128 programlama kartının resimlerini görebilirsiniz.

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