Introduction
This application note applies to the MC68HC908LB8, MC68HC908QL4, MC68HC908QB4/QB8/QY8, and MC68HC908QY4A Series1 FLASH-based microcontroller units (MCUs). To program, erase, and verify FLASH, these MCUs have on-chip FLASH support routines residing in ROM (read-only memory). These routines may be accessed in either user mode or monitor mode and eliminate the need to develop separate FLASH routines for applications.

This application note describes how to call each of the routines in user software, what is performed, and what is returned as confirmation of routine execution. The software files are available as a zip file, AN2635SW, from the Freescale Semiconductor website: www.freescale.com

FLASH Overview
The FLASH cell used on these 0.5-µ MCUs is an industry-proven split-gate cell. The cell uses channel hot electron injection for programming and Fowler-Nordheim tunnelling for erasing. All programming voltages are generated internally by a charge pump from a single connection to VDD.

With the quick byte-programming time and the organization of the FLASH array into 32-byte rows, the entire 8-Kbyte memory can be programmed in less than one-half second. This type of FLASH is specified to withstand at least 10,000 program/erase cycles and has enhanced reliability over previous technology.

Usually, split-gate FLASH is programmed on a row basis and erased on a page basis. Also, an entire specified array can be mass erased. For the target MCUs, rows are 32 bytes and pages are 64 bytes (two rows of 32 bytes each).