UDATA_ACS Example

UDATA_ACS Example

Directives highlighted in this example for PIC18CXXX devices are:

• udata_acs

Program Functional Description

This program demonstrates the utility of the udata_acs directive, which is used when generating an object file. This directive declares the beginning of a section of uninitialized data.

Commented Code Listing

list p=18c452 ;Select device.

#include <p18c452.inc> ;Include standard header file

;for the selected device.

group1 udata_acs 0x20 ;group1 data stored at access

;RAM locations starting at 0x20.

group1_var1 res 1 ;group1_var1 located at 0x20.

group1_var2 res 1 ;group1_var2 located at 0x21.

group2 udata_acs ;Declaration of group2 data. The

;addresses for data under this

;secton are allocated

;automatically by the linker.

group2_var1 res 1 ;All addresses be will allocated

group2_var2 res 1 ;in access RAM space only.

RST CODE H'0' ;The code section named RST is

;placed at H'0'. The instruction

;'goto start' is placed in code

;section RST.

goto start ;Jumps to the location labelled

;'start'

INTRT CODE H'8' ;The code section named INTRT is

;placed at H'4'. The instruction

;'goto service_int' is placed in

;code section INTRT.

goto service_int ;Jumps to the location labelled

;'service_int'.

PGM CODE ;This is the begining of the code

;section named PGM. It is a

;relocatable code section since

;no absolute address is given along

;with directive 'CODE'.

start

clrf group1_var1,A ;group1_var1 initialized to zero

clrf group1_var2,A ;group1_var2 initialized to zero

clrf group2_var1,A ;group2_var1 initialized to zero

clrf group2_var2,A ;group2_var2 initialized to zero

goto $

service_int

retfie

end