C and the 8051

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C and the 8051

• EGRE 631

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Introduction

• The Silicon Labs ISE uses the Keil C51 compiler.
• The code size is limiter to 2K
• C has replaced PL/M (the original Intel high
  level language (HLL) for imbedded systems).
• Versions of basic and a few other HLL such as
  FOUTH are available for the 8051.
• The Keil C51 is a complete implementation of ANSI
  C with extensions.
• The extensions support various features of the
  8051.
• See Chapter 3 of the C51 compiler manual. See
  c51.pdf at the bottom of the class web page.

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Example program

• include ltc8051f020.hgt // SFR declarations
• extern unsigned char rd_buttons(void) // in
  uni.c
• unsigned char mbtn()
• unsigned char last_button
• last_button last_button rd_buttons()
• P1 P1 0x01 //Set P1.0
• P1 P1 0x40 //Toggle P1.7
• P1 P1 0x40 //Set P1.7
• return(last_button)

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The Cx51 compiler generates a number of output
files during compilation. Bydefault, each of
these output files shares the same filename as
the source file.

• filename.LST Files with this extension are
  listing files that contain the formatted source
• text along with any errors detected by the
  compiler. Listing files may
• optionally contain the symbols used and the
  assembly code generated.
• For more information, refer to the PRINT
  directive in the following sections.
• filename.OBJ Files with this extension are object
  modules that contain relocatable object
• code. Object modules may be linked to an absolute
  object module by the
• Lx51 Linker/Locator.
• filename.I Files with this extension contain the
  source text as expanded by the
• preprocessor. All macros are expanded and all
  comments are deleted in
• this listing. For more information, refer to the
  PREPRINT directive in the
• following sections.
• filename.SRC Files with this extension are
  assembly source files generated from your C
• source code. These files can be assembled with
  the A51 assembler. For
• more information, refer to the SRC directive in
  the following sections.

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mbtn.lst
1 include ltc8051f020.hgt
// SFR declarations 2 extern
unsigned char rd_buttons(void) // in uni.c 3
unsigned char mbtn() 4 5
1 unsigned char last_button 6 1
last_button last_button rd_buttons()
7 1 P1 P1 0x01 //Set P1.0 8
1 P1 P1 0x40 //Toggle P1.7 9 1
P1 P1 0x40 //Set P1.7 10 1
return(last_button) 11 1 MODULE
INFORMATION STATIC OVERLAYABLE CODE SIZE
18 ---- CONSTANT SIZE ----
---- XDATA SIZE ---- ----
PDATA SIZE ---- ---- DATA SIZE
---- 1 IDATA SIZE ----
---- BIT SIZE ---- ---- END
OF MODULE INFORMATION.
18 bytes of code
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mbtn.lst
1 include ltc8051f020.hgt
// SFR declarations 2 extern
unsigned char rd_buttons(void) // in uni.c 3
unsigned char mbtn() 4 5
1 unsigned char last_button 6 1
last_button last_button rd_buttons()
7 1 P1 P1 0x01 //Set P1.0 8
1 P1 P1 0x40 //Toggle P1.7 9 1
P1 P1 0x40 //Set P1.7 10 1
return(last_button) 11 1 ASSEMBLY
LISTING OF GENERATED OBJECT CODE FUNCTION mbtn
(BEGIN)
SOURCE LINE 3
SOURCE LINE 4
SOURCE LINE 6 0000
120000 E LCALL rd_buttons 0003 EF
MOV A,R7 0004 4200 R ORL
last_button,A 0006 439001 ORL
P1,01H SOURCE LINE 7 0009 639040
XRL P1,040H SOURCE LINE 8 000C 439040
ORL P1,040H SOURCE LINE 9 000F
AF00 R MOV R7,last_button SOURCE
LINE 10 0011 ?C0001 0011 22
RET SOURCE LINE 11
FUNCTION mbtn (END) MODULE INFORMATION STATIC
OVERLAYABLE CODE SIZE 18 ----
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mbtn.lst
1 pragma CODE 2
include ltc8051f020.hgt // SFR
declarations 3 extern unsigned char
rd_buttons(void) // in uni.c 4
unsigned char mbtn() 5 6 1
unsigned char last_button 7 1
last_button last_button rd_buttons() 8
1 P1 P1 0x01 //Set P1.0 9 1
P1 P1 0x40 //Toggle P1.7 10 1
P1 P1 0x40 //Set P1.7 11 1
return(last_button) 12 1 ASSEMBLY
LISTING OF GENERATED OBJECT CODE FUNCTION mbtn
(BEGIN) 0000 120000 E LCALL
rd_buttons 0003 EF MOV
A,R7 0004 4200 R ORL
last_button,A
SOURCE LINE 8 0006 439001
ORL P1,01H
SOURCE LINE 9 0009 639040
XRL P1,040H
SOURCE LINE 10 000C 439040
ORL P1,040H
SOURCE LINE 11 000F AF00 R
MOV R7,last_button
SOURCE LINE 12 0011
?C0001 0011 22 RET
FUNCTION mbtn (END)
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1 pragma CODE 2 pragma SRC 3
include ltc8051f020.hgt //
SFR declarations 4
RSEG ?PR?mbtn?MBTN mbtn USING 0 SOURCE
LINE 5 SOURCE LINE 6 unsigned
char last_button last_button last_button
rd_buttons() SOURCE LINE
8 LCALL rd_buttons MOV A,R7 ORL
last_button?040,A P1 P1 0x01 //Set
P1.0 SOURCE LINE 9 ORL P1,01H P1
P1 0x40 //Toggle P1.7 SOURCE LINE
10 XRL P1,040H P1 P1 0x40 //Set
P1.7 SOURCE LINE 11 ORL P1,040H
return(last_button) SOURCE LINE 12 MOV
R7,last_button?040 SOURCE LINE
13 ?C0001 RET END OF mbtn
mbtn.src
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Inline assembly language Use SRC pragma this
suppresses .obj file. Must assemble .src file to
generate .obj file.
pragma CODE pragma SRC include ltc8051f020.hgt
// SFR declarations extern unsigned
char rd_buttons(void) // in uni.c unsigned char
mbtn() unsigned char last_button
last_button last_button rd_buttons() pragma
asm SETB P1.0 // P1 P1 0x01 //Set
P1.0 CPL P1.7 // P1 P1 0x40 //Toggle
P1.7 SETB P1.7 // P1 P1 0x40 //Set
P1.7 pragma endasm return(last_button)
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sbit - provides access to bit-addressable SFRs
and other bit-addressable objects. For example
sbit EA 0xAF The expression to the right of
the equal sign () specifies an absolute bit
address for the symbolic name. There are three
variants for specifying the address Variant 1
sfr_name int_constant This variant uses a
previously declared sfr (sfr_name) as the base
address for the sbit. The expression following
the carat symbol () specifies the position of
the bit to access with this declaration. The bit
position must be a number in the 0 to 7 range.
For example sfr PSW 0xD0 sbit OV PSW
2 sbit CY PSW 7 Variant 2 int_constant
int_constant This variant uses an integer
constant as the base address for the
sbit. example sbit OV 0xD0 2 sbit CY 0xD0
7 sbit EA 0xA8 7 Variant 3 int_constant
This variant uses an absolute bit address for the
sbit. For example sbit OV 0xD2 sbit EA 0xAF
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pragma CODE include ltc8051f020.hgt
// SFR declarations extern unsigned char
rd_buttons(void) // in uni.c sbit P1_0 P10
sbit P1_7 P17 unsigned char mbtn()
unsigned char last_button // sbit P1_0 P10
// sbit cannot be declared local // sbit P1_7
P17 // it must be global last_button
last_button rd_buttons() P1_0 1 P1_7
P1_7 P1_7 1 return(last_button)
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ASSEMBLY LISTING OF GENERATED OBJECT CODE
FUNCTION mbtn (BEGIN) 0000 120000 E
LCALL rd_buttons 0003 EF MOV
A,R7 0004 4200 R ORL
last_button,A 0006 D290 SETB
P1_0 0008 B297 CPL P1_7 000A
D297 SETB P1_7 000C AF00 R
MOV R7,last_button 000E
?C0001 000E 22 RET
FUNCTION mbtn (END) MODULE INFORMATION
STATIC OVERLAYABLE CODE SIZE 15
---- CONSTANT SIZE ---- ----
XDATA SIZE ---- ---- PDATA SIZE
---- ---- DATA SIZE ----
1 IDATA SIZE ---- ----
BIT SIZE ---- ---- END OF MODULE
INFORMATION. C51 COMPILATION COMPLETE. 0
WARNING(S), 0 ERROR(S)
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Pointers
Generic Pointers - Generic pointers are declared
in the same fashion as standard C pointers. For
example char s / string ptr / int numptr
/ int ptr / long state / Texas / Generic
pointers are stored using three bytes. The first
byte is the memory type, the second is the
high-order byte of the offset, and the third is
the low-order byte of the offset. Generic
pointers may be used to access any
variable regardless of its location in 8051
memory space. Memory-specific pointers -
include a memory type specification in
the pointer declaration and always refer to a
specific memory area. For example char data
str / ptr to string in data / int xdata
numtab / ptr to int(s) in xdata / long code
powtab / ptr to long(s) in code / Because the
memory type is specified at compile-time, the
memory type byte required by generic pointers is
not needed by memory-specific pointers. Memory-spe
cific pointers can be stored using only one byte
(idata, data, bdata, and pdata pointers) or two
bytes (code and xdata pointers).
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See HW 11.doc on class web page