EQU and #define - Electronic Circuits Projects Diagrams Free

simrantogether · 16th January 2008, 01:37 PM

Hi all,

I wanted to ask in assembly of pic - the difference between EQU and # define.

EQU I understood but confusion in # define as the following line in book says...

" A #define on the other hand tells the assembler to substitute two values where it finds a certain word e.g. #define led portb.4

Wherever the assembler finds the word led, it substitutes 6.4 (or portb.4) in it's place. "

Can anyone make me understand above statement...

Main thing i understood that # define is used as generic - that we can make changes only at one part of program and all the program the values shall be changed automatically...

Regards,

Simran..

geko · 16th January 2008, 03:33 PM

#define led portb.4

Anywhere mpasm finds the word 'led' it will substitute the string 'portb.4'

The part about '6.2' is simply because somwhere else 'portb' has already been set (probably in the procesor INC file) using portb EQU 6 - Why six? Because 6 is the address of portb in the data memory area.

bananasiong · 16th January 2008, 03:36 PM

Hi,
#define can be used for instructions, such as

Code:

#define on bsf PORTB, 0
#define off bcf PORTB, 0

but equ is often used for values, such as the address location of the general purpose registers.

These are my applications for equ and #define

simrantogether · 17th January 2008, 05:52 AM

Hi Geko and Bananasiong...

Thanks... I understood...

One last question...

EQU has two purposes... 1. Assigning names to registers 2. assigning values to variables..

Am i right...

Regards,

Simran..

bananasiong · 17th January 2008, 06:41 AM

Hi,
General purpose registers are used for storing variables as well. So basically they are the same. That equate directive is for us to differentiate the registers easier, instead of the memory location, we can equate the name.

simrantogether · 17th January 2008, 07:01 AM

Ok...

e.g.

Sam EQU #3 ; it means that sam is a variable with constant value 3 ...

and Sam EQU 3 ; it means that Sam is name given to register number 3 ...

I hope i am right because i have more practice for C than assembly...

Regards,

Simran..

Gayan Soyza · 17th January 2008, 07:05 AM

Mostly a bit can identify with a define directive

Code:

# define LED PORTB,0	;portB 0 bit is the LED

Equ mostly used for SFR or for variables

Code:

	PORTB 	equ 	06h		;SFR address is 06h
	TIME   	equ 	20h		;your GPR address is 20h

A special bit also can use the equ mark

Code:

C      EQU    0 	;carry bit is the zero bit in STATUS R

simrantogether · 17th January 2008, 07:44 AM

Quote:

Originally Posted by Gayan Soyza

Mostly a bit can identify with a define directive

Can we use # define for byte purpose...

Quote:

Originally Posted by Gayan Soyza

A special bit also can use the equ mark

C EQU 0 ;carry bit is the zero bit in STATUS R

how the compiler comes to know that C is a bit and not a byte name...

is it predefined that c always means carry in mp - assembler...

Regards,

Simran..

Gayan Soyza · 17th January 2008, 07:58 AM

Quote:

Originally Posted by simrantogether

Can we use # define for byte purpose...

Yes

Quote:

how the compiler comes to know that C is a bit and not a byte name...

Who knows.If it is a decimal value assembler detects as a decimal value.If its a hex thing firstly assembler searching if its a own SFR or not.

Quote:

is it predefined that c always means carry in mp - assembler...

If you write your own self contain register programs without include file for different PICs you will understand this.You need to equal the SFR as well. If you call the include file no need equal.But need to equal the other GPR's or use cblock.

**Nigel Goodwin** · 17th January 2008, 10:38 AM

Quote:

Originally Posted by simrantogether

Can we use # define for byte purpose...

how the compiler comes to know that C is a bit and not a byte name...

It doesn't need to 'know', it's simply a text substitution (both equ and define), the assembler first runs through the code and replaces all occurances of ' C ' with ' 0 ' as you told it to - there's no such thing as bits or bytes, just ASCII text.

People seem to find equ and define difficult to understand?, but when you realise it's just a simple text substitution it becomes easy - think 'search and replace' from your word processor.

simrantogether · 17th January 2008, 11:11 AM

I got it sir...

EQU is simply to match the register with its name..

and #define is almost same but we can actually give name to particular pins also...

Problem was that - I misread one statement in Book...

It was written '#define led Portb.6' while i read it as ' #define led Portb,6 '

Hence i got confused...

Regards,

Simran..

atferrari · 17th January 2008, 11:26 AM

This is from a file I am currently using (note the comma):

#DEFINE LED_RED LATA,1
#DEFINE LED_GREEN LATA,2
#DEFINE LED_YELLOW LATA,3

simrantogether · 17th January 2008, 11:29 AM

Quote:

Originally Posted by atferrari

This is from a file I am currently using (note the comma):

#DEFINE LED_RED LATA,1
#DEFINE LED_GREEN LATA,2
#DEFINE LED_YELLOW LATA,3

Hi,

Do we have to put comma or Dot ... This is the main question...

Note that in embedded C we usually put ' Dot ' ..

Regards,

Simran..

**Nigel Goodwin** · 17th January 2008, 12:00 PM

And what do you put in PIC assembler?, bear in mind this is simply a text substitution - substituting the wrong instructions isn't going to work.

simrantogether · 17th January 2008, 12:25 PM

That means we are to put comma...

I'll remember...

Regards,

Simran..

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Title	Starter	Forum	Replies	Latest
Substituting a 16x2 LCD display for 16x1 LCD display?	Dawny	Electronic Projects Design/Ideas/Reviews	19	11th October 2008 09:58 AM
Help needed ASM to HEX with MPLAB	Virus	Micro Controllers	39	26th December 2007 04:30 PM
PIC12f675	MERV	Micro Controllers	18	10th December 2007 08:18 PM
RS232 Converter	e.chain	Micro Controllers	0	6th October 2007 07:19 PM
Stepper motor circuit for PIC16f877	flemmard	Electronic Projects Design/Ideas/Reviews	6	28th September 2007 03:58 PM

16th January 2008, 01:37 PM	(permalink)
simrantogether	EQU and #define Hi all, I wanted to ask in assembly of pic - the difference between EQU and # define. EQU I understood but confusion in # define as the following line in book says... " A #define on the other hand tells the assembler to substitute two values where it finds a certain word e.g. #define led portb.4 Wherever the assembler finds the word led, it substitutes 6.4 (or portb.4) in it's place. " Can anyone make me understand above statement... Main thing i understood that # define is used as generic - that we can make changes only at one part of program and all the program the values shall be changed automatically... Regards, Simran.. __________________ Simran.. 8051 Specialist..

16th January 2008, 03:33 PM	(permalink)
geko	#define led portb.4 Anywhere mpasm finds the word 'led' it will substitute the string 'portb.4' The part about '6.2' is simply because somwhere else 'portb' has already been set (probably in the procesor INC file) using portb EQU 6 - Why six? Because 6 is the address of portb in the data memory area. __________________ Pete picprojects.org.uk

16th January 2008, 03:36 PM	(permalink)
bananasiong	Hi, #define can be used for instructions, such as Code: #define on bsf PORTB, 0 #define off bcf PORTB, 0 but equ is often used for values, such as the address location of the general purpose registers. These are my applications for equ and #define __________________ Superman returns..

17th January 2008, 05:52 AM	(permalink)
simrantogether	Hi ... Hi Geko and Bananasiong... Thanks... I understood... One last question... EQU has two purposes... 1. Assigning names to registers 2. assigning values to variables.. Am i right... Regards, Simran.. __________________ Simran.. 8051 Specialist..

17th January 2008, 06:41 AM	(permalink)
bananasiong	Hi, General purpose registers are used for storing variables as well. So basically they are the same. That equate directive is for us to differentiate the registers easier, instead of the memory location, we can equate the name. __________________ Superman returns..

17th January 2008, 07:01 AM	(permalink)
simrantogether	Ok... Ok... e.g. Sam EQU #3 ; it means that sam is a variable with constant value 3 ... and Sam EQU 3 ; it means that Sam is name given to register number 3 ... I hope i am right because i have more practice for C than assembly... Regards, Simran.. __________________ Simran.. 8051 Specialist..

17th January 2008, 07:05 AM	(permalink)
Gayan Soyza	Mostly a bit can identify with a define directive Code: # define LED PORTB,0 ;portB 0 bit is the LED Equ mostly used for SFR or for variables Code: PORTB equ 06h ;SFR address is 06h TIME equ 20h ;your GPR address is 20h A special bit also can use the equ mark Code: C EQU 0 ;carry bit is the zero bit in STATUS R __________________ Gayan My Website http://gsmicro.blogspot.com/

17th January 2008, 11:11 AM	(permalink)
simrantogether	I got it sir... I got it sir... EQU is simply to match the register with its name.. and #define is almost same but we can actually give name to particular pins also... Problem was that - I misread one statement in Book... It was written '#define led Portb.6' while i read it as ' #define led Portb,6 ' Hence i got confused... Regards, Simran.. __________________ Simran.. 8051 Specialist..

17th January 2008, 11:26 AM	(permalink)
atferrari	#define This is from a file I am currently using (note the comma): #DEFINE LED_RED LATA,1 #DEFINE LED_GREEN LATA,2 #DEFINE LED_YELLOW LATA,3 __________________ Agustín Tomás In theory, there is no difference between theory and practice. In practice, however, there is.

17th January 2008, 12:00 PM	(permalink)
Nigel Goodwin	And what do you put in PIC assembler?, bear in mind this is simply a text substitution - substituting the wrong instructions isn't going to work. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

17th January 2008, 12:25 PM	(permalink)
simrantogether	That means... That means we are to put comma... I'll remember... Regards, Simran.. __________________ Simran.. 8051 Specialist..