Hello,
Just to set the record straight for people trying to help, the DP256B is probably an S12 and not a HC12.
You can get the memory of the device by reading the Datasheet.
The DP256B means 256KB of flash, the rest is in the device user guide.
Note that B at the end shows an old flash technology.
It would be judicious not to use this device for new development but to prefer the MC9S12DP256 or the one with a E at the end (RoHS-Lead Free) as their flash is much better.
Regards,
Alban.