Writing Code with the C18 Compiler - Revision history

Hwang: /* Setting Up the Project */

2007-11-03T02:02:28Z

Setting Up the Project

Hwang: /* Timers and Counters */

2007-09-14T19:44:20Z

Timers and Counters

Hwang: /* Code Structure */

2007-09-14T19:43:41Z

Code Structure

Hwang: /* Code Structure */

2007-09-14T19:43:20Z

Code Structure

Hwang at 19:40, 14 September 2007

2007-09-14T19:40:41Z

Hwang: /* Baud Rates */

2007-09-11T18:56:40Z

Baud Rates

Hwang: /* USART */

2007-09-11T18:50:04Z

USART

Hwang: /* Math with Different Data Types */

2007-09-10T23:24:27Z

Math with Different Data Types

Hwang: /* Math with Different Data Types */

2007-09-10T23:24:08Z

Math with Different Data Types

Hwang at 23:23, 10 September 2007

2007-09-10T23:23:20Z

@@ Line 40: / Line 40: @@
 ==Setting Up the Project==
-'''If you are using the ICD2 programmer, be sure to follow the installation instructions carefully, or Windows may attempt to install the wrong drivers.''' If you've installed the wrong drivers, follow instructions in the user guide to remove the drivers.  After installing both MPLAB and C18, create a new project with the project wizard.  Follow the prompts, and you should end up with an empty project if you did not add any existing files.
+'''If you are using the ICD2 programmer, be sure to follow the installation instructions carefully, or Windows may attempt to install the wrong drivers.''' If you've installed the wrong drivers, follow instructions in the user guide to remove the drivers.  After installing both MPLAB and C18, create a new project with the project wizard.  Follow the prompts (be sure to choose the C18 toolsuite), and you should end up with an empty project if you did not add any existing files.
 We must now add a linker script to your project.  Make sure '''View>Project''' is checked, and that the '''Files''' tab is selected in the Project window.  Then, right-click on '''Linker Scripts''' in the project panel and click on '''Add Files...'''.  The linker scripts are in folder '''MCC18\lkr'''.  Find the file that corresponds to your microcontroller (<tt>p18f4431.h</tt> (or <tt>p18f4431i.h</tt> if you are using the ICD2 programmer) for the PIC18F4431 microcontroller).
@@ Line 49: / Line 49: @@
 [http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1406&dDocName=en010046 Documentation for the ICD2 Programmer]
 ==Configuration Bits==
 Certain configurations of the PIC, such as selecting the clock source or enabling the watchdog timer, must be set using configuration bits.  In C18, this is done using the <tt>#pragma config</tt> directive.  For example, for the PIC18F4431, the line <pre>#pragma config OSC=IRC</pre> tells the PIC to use the internal oscillator and set pin RA6 as the clock output.  You can put multiple bit settings on one line, for example, <pre>#pragma config OSC=IRC, WDTEN=OFF, PWM4MX=RB5</pre>  Be aware that the configuration bits can be different for different PICs.  Check the [[media:PIC18_config_settings.pdf | PIC18 Configuration Settings Addendum]] for the different options for the configuration settings.  If your part number is not listed in the document, check the Microchip website for an updated version of this document.

@@ Line 53: / Line 53: @@
 ==Timers and Counters==
-PICs generally have several timers or counters, each with different capabilities.  For the 18F4431, Timer0, Timer1, and Timer5 can be used as counters as well as timers, while Timer2 can only be used as a timer.  The difference between using a Timer in timer mode or counter mode is simply the source of the pulses &mdash; a timer runs off the system clock, while a counter increments when it sees a rising/falling edge on a certain pin.  Timers on the PIC can only count up.  Timer2 and Timer5 can generate interrupts on a period match, so are particularly suitable for implementing a real-time operating system.  Read the datasheet for a detailed explanation for the operation of these timers.  In the datasheet, '''FOSC/4''' refers to the frequency of the system oscillator divided by four.
+PICs generally have several timers or counters, each with different capabilities.  For the PIC18F4431, Timer0, Timer1, and Timer5 can be used as counters as well as timers, while Timer2 can only be used as a timer.  The difference between using a Timer in timer mode or counter mode is simply the source of the pulses &mdash; a timer runs off the system clock, while a counter increments when it sees a rising/falling edge on a certain pin.  Timers on the PIC can only count up.  Timer2 and Timer5 can generate interrupts on a period match, so are particularly suitable for implementing a real-time operating system.  Read the datasheet for a detailed explanation for the operation of these timers.  In the datasheet, '''FOSC/4''' refers to the frequency of the system oscillator divided by four.
 ==Reading and Writing to Registers==
 The I/O ports and hardware peripherals on the PIC are controlled by SFRs, or special function registers.  The values in these registers determines the behavior of the hardware.  For example, Port B is an 8 channel digital I/O port that has corresponding SFRs TRISB, PORTB, and LATB (TRISB stands for Tri-State B, PORTB stands for Port B, and LATB stands for Latch B).  Each of these registers is eight bits long, and each bit corresponds to a certain pin (channel) on the PIC.  In this case, the least significat bit of the register affects pin RB0, and the most significant bit affects pin RB7.  To write values to SFRs, we simply treat them like a global variable.  Individual bits can usually be accessed by using the convention '''[SFR_name]bits.[bit_name]''', for example, '''PORTBbits.RB0'''.  The names of the SFRs and bits can be found in the datasheet and the header file for the PIC (e.g. <tt>p18f4431.h</tt>).

@@ Line 10: / Line 10: @@
 int someGlobalInteger;         //define global variables
 char someGlobalCharacter;
+...
 int someSubFunction(int someInput){  //define functions
@@ Line 17: / Line 18: @@
    return someValue;
 }
+...
 void main( void ){          //Code entry point

@@ Line 11: / Line 11: @@
 char someGlobalCharacter;
+int someSubFunction(int someInput){  //define functions
-void main( void ){             //Code entry point
+   ...
-   OSCCON = 0b11111111;        //Configure oscillator, if needed
+   ...
-   TRISA  = 0b11110000;        //Configure ports as input or output
+   ...
-   TRISB  = 0b00000000;        //Configure unused ports as output to prevent floating inputs
+   return someValue;
-   ANSEL0 = 0b00000000;        //Set input ports as analog or digital inputs
+}
+void main( void ){          //Code entry point
+   OSCCON = 0b11111111;     //Configure oscillator, if needed
+   TRISA  = 0b11110000;     //Configure ports as input or output
+   TRISB  = 0b00000000;     //Configure unused ports as output to prevent floating inputs
+   ANSEL0 = 0b00000000;     //Set input ports as analog or digital inputs
    ANSEL1 = 0b00000000;
-   LATA   = 0b00000000;        //Set initial conditions for output ports
+   LATA   = 0b00000000;     //Set initial conditions for output ports
    LATB   = 0b11111111;
-   ...                         //Configure other peripherals like PWM, QEI, interrupts, etc.
+   ...                      //Configure other peripherals like PWM, QEI, interrupts, etc.
-   while(1){                   //Main program loop.  PIC will execute loop until reset.
+   while(1){                //Main program loop.  PIC will execute loop until reset.
+      ...
-      ...                      //Put code here.
+      ...                   //Put code here.
+      ...
    }
 }
 </pre>
 ==Setting Up the Project==
 '''If you are using the ICD2 programmer, be sure to follow the installation instructions carefully, or Windows may attempt to install the wrong drivers.''' If you've installed the wrong drivers, follow instructions in the user guide to remove the drivers.  After installing both MPLAB and C18, create a new project with the project wizard.  Follow the prompts, and you should end up with an empty project if you did not add any existing files.

@@ Line 1: / Line 1: @@
+==Code Structure==
+A basic PIC program usually has a structure similar to the following:
+<pre>
+#include <p18xxxxx.h>          //include header for PIC
+#include ...                   //include any other .h files needed for the project.
+...
+#pragma config OSC=IRCIO, ...  //set configuration bits
+int someGlobalInteger;         //define global variables
+char someGlobalCharacter;
+void main( void ){             //Code entry point
+   OSCCON = 0b11111111;        //Configure oscillator, if needed
+   TRISA  = 0b11110000;        //Configure ports as input or output
+   TRISB  = 0b00000000;        //Configure unused ports as output to prevent floating inputs
+   ANSEL0 = 0b00000000;        //Set input ports as analog or digital inputs
+   ANSEL1 = 0b00000000;
+   LATA   = 0b00000000;        //Set initial conditions for output ports
+   LATB   = 0b11111111;
+   ...                         //Configure other peripherals like PWM, QEI, interrupts, etc.
+   while(1){                   //Main program loop.  PIC will execute loop until reset.
+      ...                      //Put code here.
+   }
+}
+</pre>
 ==Setting Up the Project==
 '''If you are using the ICD2 programmer, be sure to follow the installation instructions carefully, or Windows may attempt to install the wrong drivers.''' If you've installed the wrong drivers, follow instructions in the user guide to remove the drivers.  After installing both MPLAB and C18, create a new project with the project wizard.  Follow the prompts, and you should end up with an empty project if you did not add any existing files.

@@ Line 96: / Line 96: @@
 The Universal Synchronous Asynchronous Receiver Transmitter module is a serial communications module that is typically used to communicate RS-232 or RS-485 devices.  The C18's standard library has several functions that can make it easier to set up serial communications; see the [[media:Microchip_C18_libraries.pdf | C18 Compiler Libraries]] documentation for more information.
 ===Baud Rates===
-The baud rate determines how fast the device will communicate.  The baud rates for both transmitting and receiving devices must be matched.  The baud rate is usually controlled
+The baud rate determines how fast the device will communicate.  The baud rates for both transmitting and receiving devices must be matched.  Section 19.2 in the PIC18F4431 data sheet has more information on how to configure the baud rate generator.

@@ Line 52: / Line 52: @@
 unsigned char byte2 = 200;
-someInteger = (unsigned int)byte1 + (unsigned int)unsbyte2;
+someInteger = (unsigned int)byte1 + (unsigned int)byte2;
 </pre>
 The <tt>(unsigned int)</tt> keywords will cast <tt>byte1</tt> and <tt>byte2</tt> as unsigned integers before performing the operations.

@@ Line 46: / Line 46: @@
 someInteger = byte1 + byte2;
 </pre>
-In the piece of code above, the PIC will first add <tt>byte1</tt> and <tt>byte2</tt> and then assign the result to <tt>someInteger</tt>.  The <tt>unsigned char</tt> data type has a maximum value of 255, so the result of the addition will wrap back to zero and the add upwards again.  Since the wrap-around occurs at 256, the final result will be 300-256=44, even though <tt>someInteger</tt> is perfectly capable of holding the number 300.  To work around this, we can review our code like this:
+In the piece of code above, the PIC will first add <tt>byte1</tt> and <tt>byte2</tt> and then assign the result to <tt>someInteger</tt>.  The <tt>unsigned char</tt> data type has a maximum value of 255, so the result of the addition will wrap back to zero and the add upwards again.  Since the wrap-around occurs at 256, the final result will be 300-256=44, even though <tt>someInteger</tt> is perfectly capable of holding the number 300.  To work around this, we can revise our code like this:
 <pre>
 unsigned int someInteger;