Internal Memory Configuration and External Expansion - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 722

The completion of the command is indicated by the setting of the CCIF flag. An errone-
ous command write sequence will abort and set the appropriate flag. If set, the designer must
clear the ACCERR or PVIOL flags before commencing another command write sequence. By
writing a 0 to the CBEIF flag, the command sequence can be aborted after writing a word to the
EEPROM address space or after writing a command to the ECMD register and before the com-
mand is launched. Writing a 0 to the CBEIF flag in this way will set the ACCERR flag.
The sector-modify command ($60) is a two-step command, which first erases a sector (two
words) of EEPROM and then reprograms one of the words in that sector. The EEPROM sector
that is erased by the command is the sector containing the address of the aligned data write that
starts the valid command sequence. That same address is reprogrammed with the data that is
written. By launching a sector-modify command and then pipelining a program command, it is
possible to completely replace the contents of an EEPROM sector.

Example 14.10
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Write a function that erases a sector (4 bytes) of EEPROM. Index register X contains a word-
aligned EEPROM address within the sector to be erased.
Solution: The following assembly function erases the specified EEPROM sector by following
the three-step procedure:
eraseEEsector

movb #ACCERR 1 PVIOL,ESTAT ; clear error flags

brclr ESTAT,CBEIF,EERErr ; command buffer not empty, return

std 0,X ; write any data to EEPROM sector

movb #SectorErase,ECMD ; write sector-erase command

movb #CBEIF,ESTAT ; launch erase command

brclr ESTAT,ACCERR+PVIOL,EEROK ; no error?

EERErr ldab #1 ; error code set to 1

rts

EEROK brclr ESTAT,CCIF,EEROK ; wait until command completion

clrb

rts

The C language version of the function is as follows:
int eraseEEsector (int *ptr)
{

ESTAT 5 ACCERR | PVIOL; // clear error flags

if(!(ESTAT & CBEIF))

return 1; // command buffer not empty, can't issue new command

*ptr 5 0x00; // write any data to EEPROM sector location

ECMD 5 SectorErase; // write sector-erase command

ESTAT 5 CBEIF; // launch the command

if(ESTAT & (ACCERR | PVIOL))

return 1; // error occurred

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

return 0; // command completed correctly

}

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