"1. Label
IDATALEN EQU 80H ; the length of IDATA memory in bytes.
Here idatalen is just a label, which is not the same as IData! If you like, you can change the idatalen in this program into dog, pig and Playboy (in fact, my ideal is to live a pig like life without worrying about food and drink, carefree, but I can't do it). The above sentence means that where idatalen is used in the program, it can actually be regarded as the number 80h, You are absolutely right to use 80h instead of idatalen.
The name idatalen is only used to make it easy to remember, indicating that it has a little relationship with IData, so that your program is not too long. If you used Playboy as the label, you will forget what Playboy means later. The range of IData is 0 ~ FFH. If you want to change to FFH, you can.
2。 Clear
IF IDATALEN <> 0
MOV R0,#IDATALEN - 1
CLR A
IDATALOOP: MOV @R0,A
DJNZ R0,IDATALOOP
For this paragraph, it is obvious that it is clearing. If idatalen = 80h above, it is clearing 0 ~ 7FH; If
Your program is rewritten as:
IDATALEN EQU 0100H ;
It is to clear 0 ~ FFH.
Also note the if statement, which will be discussed later.
2、 How to load this program as you wish
Generally, considering this, it is often necessary to distinguish between power on reset and program reset in your design. Sometimes when the program is reset, you don't want some memory units to be cleared, so you can't do it without making some changes to startup.a51.
The default is to automatically load this section of startup.a51.
So you have to do this:
Copy the original startup.a51 file in the Lib directory to the directory where your project is located, and then add the startup.a51 in your project directory to your project (in keil's integrated environment, I hope you know how to do this), and then modify the startup.a51.
For example, change to:
IDATALEN EQU 00H ; the length of IDATA memory in bytes.
Then compile the link. In this way, your program will not contain the internal code to reset IData.
Why? The function of the if statement mentioned above! When idatalen = 0 is defined, the reset code is skipped!
////////////////////////////////////////////
Chinese description of startup.a51
;------------------------------------------------------------------------------
; Startup.a51: user power on initialization program
;------------------------------------------------------------------------------
;
; User defined memory space for power on initialization
;
; Use the following equ command to define the memory space to be initialized with 0 during CPU reset
;
;; ; The absolute starting address of the space of IData memory is always 0;
IDATALEN EQU 80H ; The number of bytes of IData memory space that needs to be initialized with 0
;
XDATASTART EQU 0H ; Absolute starting address of XDATA storage space
XDATALEN EQU 0H ; The number of space bytes of XDATA memory to initialize with 0
;
PDATASTART EQU 0H ; Absolute starting address of the space of pdata memory
PDATALEN EQU 0H ; The number of space bytes of pdata memory to be initialized with 0
;
; Note: the space of IData memory physically includes the data and bit memory space of 8051 single chip microcomputer
; It is said that at least the memory space related to the C51 compiler runtime should be 0 initialized. Do you want to
;------------------------------------------------------------------------------
;
; Reentry function simulation initialization
;
; The following defines the reentry function with the equ instruction to simulate the initialization of the stack pointer
;
; The stack space of the reentry function when using small memory mode
IBPSTACK EQU 0 ; When using the small memory mode reentry function, set it to 1
IBPSTACKTOP EQU 0FFH+1 ; Set the top of the stack to the highest address + 1
;
; Stack space of reentry function when using large memory mode; The stack space of the reentry function when using the large memory mode
XBPSTACK EQU 0 ; When using the large memory mode reentry function, set it to 1
XBPSTACKTOP EQU 0FFFFH+1; Set the top of the stack to the highest address + 1
;
; Stack space of reentry function when compact memory mode is used; The stack space of the reentry function when using compact memory mode
PBPSTACK EQU 0 ; Set the compact memory mode reentry function to 1
PBPSTACKTOP EQU 0FFFFH+1; Set the top of the stack to the highest address + 1
;
;------------------------------------------------------------------------------
;
; Paging definition of 64K byte XDATA memory space when using compact memory mode
;
; The following uses the equ instruction to define the page address of pdata type variable in XDATA memory space
; When defining pfage with equ command, it must be consistent with the control parameters of L51 connection locator pdata command
;
PPAGEENABLE EQU 0 ; When using a pdata type variable, set it to 1
PPAGE EQU 0 ; Define page number
;
;------------------------------------------------------------------------------
NAME ? C_ STARTUP; Module name is? C_ STAUTUP
? C_ C51STARTUP SEGMENT CODE ; code
? STACK SEGMENT IDATA ; stack
RSEG ? STACK ; stack
DS 1
EXTRNEXTRN CODE ((? C_ START)) ; Program start address
PUBLIC ? C_ STARTUP
CSEG AT 0x8000 ; Defining the starting address of the user program may be useful when using the mon51 emulator
? C_ STARTUP: LJMP STARTUP1
RSEG ? C_ C51STARTUP
STARTUP1::
;
; Initialize serial port
MOV SCON,#40H
MOV TMOD,#20H
MOV TH1,#0fdH
SETB TR1
CLR TI
; When the MCU is powered on, the IData memory is cleared. If it is not necessary to power on, the IData can log off the words between if and ifedn
; Or modify the length of the idtalen. In order to have the power down protection function, I don't know how long the idtalen is
IF IDATALEN <> 0
MOV R0,#IDATALEN - 1
CLR A
IDATALOOP: MOV @R0,A
DJNZ R0,IDATALOOP
ENDIF
;
; MCU power on XDATA memory reset if you do not need power on to reset XDATA, you can log off the words between if and ifedn
; Or modify the length of xdatalen
IF XDATALEN <> 0
MOV DPTR,#XDATASTART
MOV R7,#LOW ((XDATALEN)
IF (LOW (XDATALEN) <> 0
MOV R6,#(HIGH (XDATALEN) +1
ELSE
MOV R6,,#HIGH ((XDATALEN)
ENDIF
CLR A
XDATALOOP: MOVX @DPTR,A
INC DPTR
DJNZ R7,XDATALOOP
DJNZ R6,XDATALOOP
ENDIF
;
; Send pdata memory page high address
IF PAGEENABLE <> 0
MOV P2,#PPAGE
ENDIF
;
; When the MCU is powered on, pdata memory is cleared. If it is not necessary to power on, XDATA can log off the words between if and ifedn
; Or modify the length of pdatalen
IF PDATALEN <> 0
MOV R0,#PDATASTART
MOV R7,#LOW (PDATALEN)
CLR A
PDATALOOP: MOVX @R0,A
INC R0
DJNZ R7,PDATALOOP
ENDIF
;
; Sets the stack space for reentry functions when using small memory mode
IF IBPSTACK <> 0
EXTRN DATA (? C_ IBP)
MOV ? C_ IBP,#LOW IBPSTACKTOP
ENDIF
;
; Sets the stack space for reentry functions when using large memory mode
IF XBPSTACK <> 0
EXTRN DATA (? C_ XBP)
MOV ? C_ XBP,#HIGH XBPSTACKTOP
MOV ? C_ XBP+1,#LOW XBPSTACKTOP
ENDIF
;
; Sets the stack space for reentry functions when compact memory mode is used
IF PBPSTACK <> 0
EXTRN DATA (C_ PBP)
MOV ? C_ PBP,#LOW PBPSTACKTOP
ENDIF
;
; Sets the starting address of the stack
MOV SP,#? STACK-1 ; For example, MOV SP, #4fh;
; This code is required if you use L51_ BANK.A51 with Banking Mode 4
; If your program uses mode 4 program grouping technology, please start the following program. Your program will not exceed 64K
; EXTRN CODE (? B_ SWITCH0)
; CALL ? B_ SWITCH0 ; init bank mechanism to code bank 0
;; The program starts from the first group of bank 0 blocks
; Jump to user program main function
LJMP ? C_ START
END
; Linshengfeng, read the full text, original title: detailed explanation of the contents of MCU startup.a51 file
Source: [micro signal: wujianying]_ Danpianji, WeChat official account: SCM Wu Jianying, please welcome to add attention! Please indicate the source of the article“
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