EmbeddedC

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07/09/11 Microcontroller 1

Embedded CEmbedded C

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The development processThe development process

Plan tasks and interactionPlan tasks and interaction

Setup overall project fileSetup overall project file

EditEdit

Project.PRJProject.PRJ

Task1.A51Task1.A51 Task2.CTask2.C

reviserevise

11 22

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Task1.A51Task1.A51 Task2.CTask2.C

AssembledAssembledCompiled andCompiled andassembledassembled

Task1.lstTask1.lst

Task2.lstTask2.lst

Link/LocateLink/LocateVarious.libVarious.lib Project.M51Project.M51

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Link/LocateLink/LocateVarious.libVarious.lib Project.M51Project.M51

Project.hexProject.hexBurn in EPROM orBurn in EPROM ordownloaddownload

reviserevise

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Intel HEX formatIntel HEX format

Example:Example:

:10400000755AFF111675907F11167590BF111675B0:10400000755AFF111675907F11167590BF111675B0

:10401000903F111680EA780379007A00DAFED9FA27:10401000903F111680EA780379007A00DAFED9FA27

:03402000D8F622AD:03402000D8F622AD

:00000001FF:00000001FF

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An ExampleAn Example

#include#include#include #include

void main(void) {void main(void) {

}}

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Development ToolsDevelopment Tools

DebuggingDebugging SimulatorSimulator

becomes less useful when there isbecomes less useful when there is

a lot of time critical hardwarea lot of time critical hardwareDownload to a target with aDownload to a target with amonitormonitor

Disadvantages: serial port is tiedDisadvantages: serial port is tiedup for downloadingup for downloading

need for a softwareneed for a software

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Development ToolsDevelopment Tools

InIn--circuit emulatorcircuit emulator

combines monitor and simulatorcombines monitor and simulator

functionsfunctions

emulator plugs into the socket whereemulator plugs into the socket where

the final processor would residethe final processor would reside

CostlyCostly

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What Language To Use for EmbeddedWhat Language To Use for EmbeddedApplicationsApplications

Assembly Assembly -- Most efficientMost efficient

but difficult to read and maintainbut difficult to read and maintain

CC

C++C++

JavaJava

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Why CWhy C

Can control many machine level functionsCan control many machine level functions

without resorting to assembly languagewithout resorting to assembly language

Application can be written in C more easilyApplication can be written in C more easily

than assembly language because thethan assembly language because the

development software manages the detailsdevelopment software manages the details

because of modularity,reusable codes can bebecause of modularity,reusable codes can bedeveloped and maintaineddeveloped and maintained

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Memory Areas

Code memory (program memory).

External data memory.

Internal data memory.

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Memory Areas

Internal data memory:>read from or written to.

>faster than any other memory.

>memory specifiers

data

idata

bdata

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Memory TypesMemory Types

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Memory TypesMemory Types

Frequently used variables are put inFrequently used variables are put in

the internal memory in preference tothe internal memory in preference to

the external RAMthe external RAM By including a memory type specifierBy including a memory type specifier

in the variable declaration, you canin the variable declaration, you can

specify where variables are storedspecify where variables are stored

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ExampleExample

char data var1;char data var1;

char code text[] = "ENTER PARAMETER:";char code text[] = "ENTER PARAMETER:";

unsigned long xdata array[100];unsigned long xdata array[100];

float idata x,y,z;float idata x,y,z;unsigned int pdata dimension;unsigned int pdata dimension;

char bdata flags;char bdata flags;

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Memory ModelsMemory Models

SMALL :SMALL : all variables default to the internal dataall variables default to the internal data

memory of the 8051memory of the 8051

same as if t

hey were declared explicitly usingsame as if th

ey were declared explicitly usingthe data memory type specifierthe data memory type specifier

variable access is very efficientvariable access is very efficient

However, all data objects, as well as theHowever, all data objects, as well as the

stack must fit into the internal RAMstack must fit into the internal RAM

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Compact:Compact: all variables default to one page of externalall variables default to one page of external

data memorydata memory

same as if t

hey were explicitly declared usingsame as if th

ey were explicitly declared usingthe pdata memory type specifierthe pdata memory type specifier

can accommodate a maximum of 256 bytes ofcan accommodate a maximum of 256 bytes of

variables as it is accessed indirectly throughvariables as it is accessed indirectly through

R0 and R1R0 and R1

variable access is not as fast as small modelvariable access is not as fast as small model

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Large:Large: all variables default to external data memoryall variables default to external data memory

same as if they were explicitly declared usingsame as if they were explicitly declared usingthe xdata memory type specifierthe xdata memory type specifier

Memory access through this data pointer isMemory access through this data pointer is

inefficient, especially for variables with ainefficient, especially for variables with alength of two or more byteslength of two or more bytes

This type of data access generates more codeThis type of data access generates more codethan the small or compact modelsthan the small or compact models

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Key differences between C and Keil CKey differences between C and Keil C

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Key differences between C and Keil CKey differences between C and Keil C

The sbit, sfr, and sfr16 data types areThe sbit, sfr, and sfr16 data types are

included to allow access to the specialincluded to allow access to the special

function registers that are available onfunction registers that are available on

the 8051the 8051 E.g: the declaration:E.g: the declaration: sfr P0 = 0x80sfr P0 = 0x80

declares the variabledeclares the variable P0P0 and assigns it theand assigns it the

special function register address ofspecial function register address of 0x800x80..This is the address of PORT 0 on the 8051.This is the address of PORT 0 on the 8051.

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Default memory typeDefault memory type

If the memory type specifier is omitted in aIf the memory type specifier is omitted in avariable declaration, the default or implicitvariable declaration, the default or implicit

memory type is automatically selectedmemory type is automatically selected

Function arguments and automatic variablesFunction arguments and automatic variables

which cannot be located in registers are alsowhich cannot be located in registers are also

stored in the default memory areastored in the default memory area

The default memory type is determined by theThe default memory type is determined by the

SMALL, COMPACT and LARGE compiler controlSMALL, COMPACT and LARGE compiler controldirectivesdirectives

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An ExampleAn Example 8 switches are connected to P08 switches are connected to P0 8 LEDs are connected to P28 LEDs are connected to P2#include #include void msec (unsigned int);void msec (unsigned int);void main ()void main (){{

unsigned char array[10];unsigned char array[10];unsigned char I;unsigned char I;while (1)while (1)

{{for (i=0; i

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Operators

== equal to comparison= greater than or equal to

!= not equal to

> shift right

++ increment

-- decrement&& Boolean and

|| Boolean or

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Operators+= add value to

-= subtract value to

*= multiply value to

/= divide value to

|= or value to&= and value to

^= exclusive or value to

= shift value right

%= modulo divide value to

-> pointer to a structure

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Bitwise operatorsBitwise operators

Logical operationLogical operation AssemblyAssembly CC

NOT CPL A ~NOT CPL A ~

AND ANL A,# & AND ANL A,# &

OR ORL A,# |OR ORL A,# |

XOR XRL A,# ^XOR XRL A,# ^

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Assignment operatorsAssignment operators

Unique to C is the shorthandUnique to C is the shorthandrepresentation for modifying arepresentation for modifying avariable and assigning it backvariable and assigning it back

portA = portA & 0xf7;portA = portA & 0xf7;

portA &= oxf7;portA &= oxf7;

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Delay by software loopingDelay by software looping

Void msec (unsigned int x)Void msec (unsigned int x){{unsigned char j;unsigned char j;while (xwhile (x---- > 0)> 0)

{{for (j=0; j

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Accessing an array elementAccessing an array element

Unsigned int ary[20];Unsigned int ary[20];unsigned int x;unsigned int x;ary[9] =x;ary[9] =x;

While defining arrays, it has to be madeWhile defining arrays, it has to be madesure that large amounts of memory issure that large amounts of memory isnot tied upnot tied up

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PointersPointers

C51 compiler supports two different typesC51 compiler supports two different types

of pointers:of pointers:

Generic pointersGeneric pointers

Memory specific pointersMemory specific pointers

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Generic PointersGeneric Pointers

char *s;char *s; /* string ptr *//* string ptr */

int *numptr;int *numptr; /* int ptr *//* int ptr */

long *state;long *state; /* long ptr *//* long ptr */

use t

hree bytes,t

he first for t

he memory type,use t

hree bytes,t

he first for t

he memory type,the second for the highthe second for the high--order byte of the offsetorder byte of the offset

and the third for the lowand the third for the low--order byte of theorder byte of theoffsetoffset

Generic pointers may be used to access anyGeneric pointers may be used to access anyvariable regardless of its location in 8051variable regardless of its location in 8051memory space.memory space.

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Memory Specific PointersMemory Specific Pointers

char data *str;char data *str; /* ptr to string in data *//* ptr to string in data */int xdata *numtab;int xdata *numtab; /* ptr to int(s) in xdata *//* ptr to int(s) in xdata */

long code *powtab;long code *powtab; /* ptr to long(s) in code *//* ptr to long(s) in code */

can be stored using only one byte (idata,can be stored using only one byte (idata,

data, bdata, and pdata pointers) ordata, bdata, and pdata pointers) or

two bytes (code and xdata pointerstwo bytes (code and xdata pointers)

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