> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf
> Of AdiCH
> Sent: 06 April 2012 13:15
> To: piclist@mit.edu
> Subject: [PIC] Read Flash of PIC16F916
>=20
>=20
> Hi
>=20
> I try to read the flash ROM of my PIC16F916 to calculate a checksum.
> I use the MPLAB and the PICC v9.83 Compiler.
>=20
> I tried this c function:
>=20
> unsigned int ReadFlash( unsigned int address ) {
>    EEADRL =3D address%256;
>    EEADRH =3D address/256;
>    EEPGD =3D 1; // program memory
>    RD =3D 1;    // read
>    ;
>    ;
>    return EEDATH*256 + EEDATL;
> }
>=20
> and everything in assembler:
>=20
> unsigned char low3;
> unsigned char high3;
>=20
> unsigned int dataFlash;
>=20
> void main() {
>=20
>    #asm
>       BCF        _STATUS, 5
>       BCF        _STATUS, 6
>       MOVF       _low3, W
>       BSF        _STATUS, 6
>       MOVWF      _EEADR
>       BCF        _STATUS, 6
>       MOVF       _high3, W
>       BSF        _STATUS, 6
>       MOVWF      _EEADRH
>       BSF        _STATUS, 5
>       BSF        _EECON1, 7
>       BSF        _EECON1, 0
>       NOP
>       NOP
>       BCF        _STATUS, 5
>       MOVF       _EEDATH, W
>       MOVWF      _dataFlash+1
>       CLRF       _dataFlash
>       MOVF       _EEDATA, W
>       IORWF      _dataFlash, F
>       MOVLW      0
>       IORWF      _dataFlash+1, F
>    #endasm
> }
>=20
> But both are not working, if I debug it most of the time the register
> EEDATA
> and EEDATH have the right value. But if I copy it to the variable
> dataFlash
> it is 0.


I'm not surprised the assembler version is not working, the code for transf=
erring the data from EEDATH/EEDATA into 'dataflash' is visibly wrong; I hav=
e added comments below:

MOVF       _EEDATH, W		; EEDATH is now in W
MOVWF      _dataFlash+1		; EEDATH is now in MSB of 'dataflash'
CLRF       _dataFlash		; LSB of 'dataflash' is now zero
MOVF       _EEDATA, W		; EEDATA is now in W
IORWF      _dataFlash, F	; EEDATA is now in LSB of 'dataflash'
MOVLW      0			; W=3D0
IORWF      _dataFlash+1, F	; MSB of 'dataflash' is now zero.

Why not do this?

MOVF       _EEDATH, W		; EEDATH is now in W
MOVWF      _dataFlash+1		; EEDATH is now in MSB of 'dataflash'
MOVF       _EEDATA, W		; EEDATA is now in W
MOVWF      _dataFlash, F	; EEDATA is now in LSB of 'dataflash'


Please note I have not checked that your bank switching is correct; it woul=
d be much better to use macros to do this if your compiler supports this in=
 inline assembler.


In the C version it looks like you are assuming that a line that contains o=
nly a semicolon will be converted into a NOP operation, are you certain thi=
s is the case? In the compilers I use a semicolon by itself will not produc=
e any code, and you might need to use inline assembler to insert a NOP (or =
your compiler may provide a macro to do this).

Also be very careful using the modulo operator to extract high and low byte=
s from a word. A modulo operation is very expensive in terms of CPU cycles.=
  The optimiser may fix this if it notices you are doing a simple byte move=
 operation, but don't count on it.  A simple bit shift/mask is a much bette=
r idea:

EEADRL =3D address & 0xFF;
EEADRH =3D address >> 8;

Cheers

Mike

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