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Ax51 User's Guide
Ax51 Introduction 
What is an Assembler? Modular Programming Modular Program Development Process Segments, Modules, and Programs Translate and Link Process Filename Extensions Program Template File 
Assembling Programs Writing Assembly Programs Control Statements Macro Processor Error Messages AppendixProgram Template File
The following code template contains guidelines and hints on how to write your own assembly modules. This template file TEMPLATE.A51 is provided in the folder \C51\ASM.
$NOMOD51 ; disable predefined 8051 registers
#include <reg52.h> // include CPU definition file (for example, 8052)
;
; Change names in lowercase to suit your needs.
;
; This assembly template gives you an idea of how to use the A251/A51
; Assembler. You are not required to build each module this way this is only
; an example.
;
; All entries except the END statement at the End Of File are optional.
;
; If you use this template, make sure you remove any unused segment declarations,
; as well as unused variable space and assembly instructions.
;
; This file cannot provide for every possible use of the A251/A51 Assembler.
;
;
; Module name (optional)
;
NAME module_name
;
; Here, you may import symbols form other modules.
;
EXTRN CODE (code_symbol) ; May be a subroutine entry declared in
; CODE segments or with CODE directive.
EXTRN DATA (data_symbol) ; May be any symbol declared in DATA segments
; segments or with DATA directive.
EXTRN BIT (bit_symbol) ; May be any symbol declared in BIT segments
; or with BIT directive.
EXTRN XDATA (xdata_symbol) ; May be any symbol declared in XDATA segments
; or with XDATA directive.
EXTRN NUMBER (typeless_symbol); May be any symbol declared with EQU or SET
; directive
;
; You may include more than one symbol in an EXTRN statement.
;
EXTRN CODE (sub_routine1, sub_routine2), DATA (variable_1)
;
; Force a page break in the listing file.
;
$EJECT
;
; Here, you may export symbols to other modules.
;
PUBLIC data_variable
PUBLIC code_entry
PUBLIC typeless_number
PUBLIC xdata_variable
PUBLIC bit_variable
;
; You may include more than one symbol in a PUBLIC statement.
;
PUBLIC data_variable1, code_table, typeless_num1, xdata_variable1
;
; Put the STACK segment in the main module.
;
?STACK SEGMENT IDATA ; ?STACK goes into IDATA RAM.
RSEG ?STACK ; switch to ?STACK segment.
DS 5 ; reserve your stack space
; 5 bytes in this example.
$EJECT
;
; Put segment and variable declarations here.
;
;
; DATA SEGMENT Reserves space in DATA RAM Delete this segment if not used.
;
data_seg_name SEGMENT DATA ; segment for DATA RAM.
RSEG data_seg_name ; switch to this data segment
data_variable: DS 1 ; reserve 1 Bytes for data_variable
data_variable1: DS 2 ; reserve 2 Bytes for data_variable1
;
; XDATA SEGMENT Reserves space in XDATA RAM Delete this segment if not used.
;
xdata_seg_name SEGMENT XDATA ; segment for XDATA RAM
RSEG xdata_seg_name ; switch to this xdata segment
xdata_variable: DS 1 ; reserve 1 Bytes for xdata_variable
xdata_array: DS 500 ; reserve 500 Bytes for xdata_array
;
; INPAGE XDATA SEGMENT Reserves space in XDATA RAM page (page size: 256 Bytes)
; INPAGE segments are useful for @R0 addressing methodes.
; Delete this segment if not used.
;
page_xdata_seg SEGMENT XDATA INPAGE ; INPAGE segment for XDATA RAM
RSEG xdata_seg_name ; switch to this xdata segment
xdata_variable1:DS 1 ; reserve 1 Bytes for xdata_variable1
;
; ABSOLUTE XDATA SEGMENT Reserves space in XDATA RAM at absolute addresses.
; ABSOLUTE segments are useful for memory mapped I/O.
; Delete this segment if not used.
;
XSEG AT 8000H ; switch absolute XDATA segment @ 8000H
XIO: DS 1 ; reserve 1 Bytes for XIO port
XCONFIG: DS 1 ; reserve 1 Bytes for XCONFIG port
;
; BIT SEGMENT Reserves space in BIT RAM Delete segment if not used.
;
bit_seg_name SEGMENT BIT ; segment for BIT RAM.
RSEG bit_seg_name ; switch to this bit segment
bit_variable: DBIT 1 ; reserve 1 Bit for bit_variable
bit_variable1: DBIT 4 ; reserve 4 Bits for bit_variable1
;
; Add constant (typeless) numbers here.
;
typeless_number EQU 0DH ; assign 0D hex
typeless_num1 EQU typeless_number 8 ; evaluate typeless_num1
$EJECT
;
; Provide an LJMP to start at the reset address (address 0) in the main module.
; You may use this style for interrupt service routines.
;
CSEG AT 0 ; absolute Segment at Address 0
LJMP start ; reset location (jump to start)
;
; CODE SEGMENT Reserves space in CODE ROM for assembler instructions.
;
code_seg_name SEGMENT CODE
RSEG code_seg_name ; switch to this code segment
USING 0 ; state register_bank used
; for the following program code.
start: MOV SP,#?STACK 1 ; assign stack at beginning
;
; Insert your assembly program here. Note, the code below is non functional.
;
ORL IE,#82H ; enable interrupt system (timer 0)
SETB TR0 ; enable timer 0
repeat_label: MOV A,data_symbol
ADD A,#typeless_symbol
CALL code_symbol
MOV DPTR,#xdata_symbol
MOVX A,@DPTR
MOV R1,A
PUSH AR1
CALL sub_routine1
POP AR1
ADD A,R1
JMP repeat_label
code_entry: CALL code_symbol
RET
code_table: DW repeat_label
DW code_entry
DB typeless_number
DB 0
$EJECT
;
; To include an interrupt service routine, provide an LJMP to the ISR at the
; interrupt vector address.
;
CSEG AT 0BH ; 0BH is address for Timer 0 interrupt
LJMP timer0int
;
; Give each interrupt function its own code segment.
;
int0_code_seg SEGMENT CODE ; segment for interrupt function
RSEG int0_code_seg ; switch to this code segment
USING 1 ; register bank for interrupt routine
timer0int: PUSH PSW
MOV PSW,#08H ; register bank 1
PUSH ACC
MOV R1,data_variable
MOV DPTR,#xdata_variable
MOVX A,@DPTR
ADD A,R1
MOV data_variable1,A
CLR A
ADD A,#0
MOV data_variable1+1,A
POP ACC
POP PSW
RETI
;
; The END directive is ALWAYS required.
;
END ; End Of File
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