Internal Memory Configuration and External Expansion - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 712

Step 2
Write the program or erase command to the command buffer.
Step 3
Clear the CBEIF flag by writing a 1 to it to launch the command. The clearing of the CBEIF
flag indicates that the command was successfully launched. The CBEIF flag will be set
again, indicating that the address, data, and command buffers are ready for a new command
sequence to begin. A summary of the programming algorithm is shown in Figure 14.17.

Start

No

Is FDIVLD bit set?

Write FCLKDIV register

Ye s

Write array address and
program data

Write program command $20
to the FCMD register

Write $80 to register FSTAT
to clear the CBEIF bit

Ye s

Protection
violation check

Write $20 to FSTAT
to clear the PVIOL bit

Bit PVIOL
set?

No

Ye s

Write $10 to FSTAT to
clear the ACCERR bit

Access
error check

Bit ACCERR
set?

No

Address, data,
command buffer
empty check

Ye s Ye s

Next
write?

Bit CBEIF
set?

No

No

Command
completion check

No

Bit CCIF
set?

Ye s

Stop

Figure 14.17 ■ HCS12 flash memory program algorithm

If an HCS12 device has multiple flash memory blocks, we need to clear the ACCERR and
PVIOL flags in all blocks and also set the BKSEL bits in the FCNFG register properly to select
the desired block for erasure or programming.