MC9S12E256 Datasheet, PDF (81/602 Pages) Freescale Semiconductor, Inc – HCS12 Microcontrollers

Chapter 2
256 Kbyte Flash Module (FTS256K2V1)
2.1 Introduction
This document describes the FTS256K2 module that includes a 256 Kbyte Flash (nonvolatile) memory.
The Flash memory may be read as either bytes, aligned words, or misaligned words. Read access time is
one bus cycle for bytes and aligned words, and two bus cycles for misaligned words.
The Flash memory is ideal for program and data storage for single-supply applications allowing for field
reprogramming without requiring external voltage sources for program or erase. Program and erase
functions are controlled by a command driven interface. The Flash module supports both block erase and
sector erase. An erased bit reads 1 and a programmed bit reads 0. The high voltage required to program
and erase the Flash memory is generated internally. It is not possible to read from a Flash block while it is
being erased or programmed.
CAUTION
A Flash word must be in the erased state before being programmed.
Cumulative programming of bits within a Flash word is not allowed.
2.1.1 Glossary
Banked Register — A memory-mapped register operating on one Flash block which shares the same
register address as the equivalent registers for the other Flash blocks. The active register bank is selected
by the BKSEL bit in the FCNFG register.
Command Write Sequence — A three-step MCU instruction sequence to execute built-in algorithms
(including program and erase) on the Flash memory.
Common Register — A memory-mapped register which operates on all Flash blocks.
MC9S12E256 Data Sheet, Rev. 1.08
Freescale Semiconductor
81