Internal Memory Configuration and External Expansion - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 724

programmed. A 0 is returned in accumulator B if the command is performed correctly; other-
wise, a 1 is returned.
Solution: The function that performs the specified function is as follows:
eeprogram

movb #ACCERR 1 PVIOL,ESTAT ; clear error flags

brclr ESTAT,CBEIF,cantPRE ; command buffer not empty

std 0,x ; write data to EEPROM address

movb #Program,ECMD ; write the command

movb #CBEIF,ESTAT ; launch the erase and check command

brclr ESTAT,ACCERR 1 PVIOL,EEPROK

cantPRE ldab #1 ; return error code 1

rts

EEPROK brclr ESTAT,CCIF,EEPROK ; wait until command is done

clrb ; successful program code is 0

rts

The C language version of the function is as follows:
int eeprogram (unsigned int data, unsigned int *ptr)
{

ESTAT 5 ACCERR 1 PVIOL; // clear error flag

if(!(ESTAT&CBEIF))

return 1;

*ptr 5 data; // write data to word-aligned address

ECMD 5 Program; // write program command

ESTAT 5 CBEIF; // launch command

if(ESTAT &(ACCERR|PVIOL))

return 1;

while(!(ESTAT&CCIF)); // wait for command to complete

return 0;

}

▲

Example 14.14
▼

Write a function that executes the sector-modify command to change the contents of an
EEPROM sector. The index register X holds the word-aligned address of the first EEPROM word
to be modified. The index register Y holds the word-aligned address of the first word of data to
be programmed.
Solution: The assembly function that performs the desired function is as follows:
eesectormodify

movb #ACCERR 1 PVIOL,ESTAT ; clear error flags

brclr ESTAT,CBEIF,cantmod ; command buffer not empty

movw 0,Y,0,X ; write data to EEPROM address

movb #SectorModify,ECMD ; write sector-modify command

movb #CBEIF,ESTAT ; launch the erase and check command

brclr ESTAT,ACCERR 1 PVIOL,EEModOK

cantmod ldab #1 ; return error code 1

rts