Stable In-circuit Programming of Flash Memory in Freescale´s MC9S12 MCU Family

In-circuit programming of flash memory in user mode (U-ICP) is a technique useful for updating in-circuit programs, providing power-off protection and the recovery of important parameters, and modifying the static parameters in embedded applications. Restrictions on manufacturing technology require U-ICP to be done at high voltage, however, which can result in the read operation becoming unstable. This phenomenon introduces specific design requirements for any in-circuit programming module. We have studied the structure of flash memory from Freescale´s MC9S12 MCU family, and devise a new scheme to solve the instability problem. We describe how to implement this scheme in detail, providing C program examples to illustrate its feasibility.