MC68HC908AT32 Datasheet, PDF (57/378 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 5
Electrically Erasable Programmable ROM (EEPROM)
5.1 Introduction
This section describes the electrically erasable programmable read-only memory (EEPROM).
5.2 Features
EEPROM features include:
• Modular architecture expandable in 128 bytes
• Byte, block, or bulk erasable
• Non-volatile redundant array option
• Non-volatile block protection option
• Non-volatile microcontroller unit (MCU) configuration bits
• On-chip charge pump for programming/erasing
• Security option
5.3 Functional Description
The 512 bytes of EEPROM can be programmed or erased without an external voltage supply. The
EEPROM has a lifetime of 10,000 write-erase cycles in the non-redundant mode. Reliability (data
retention) is further extended if the redundancy option is selected. EEPROM cells are protected with a
non-volatile block protection option. These options are stored in the EEPROM non-volatile register
(EENVR) and are loaded into the EEPROM array configuration register after reset (EEACR) or a read of
EENVR. Hardware interlocks are provided to protect stored data corruption from accidental
programming/erasing.
5.3.1 EEPROM Programming
The unprogrammed state is a logic 1. Programming changes the state to a logic 0. Only valid EEPROM
bytes in the non-protected blocks and EENVR can be programmed. When the array is configured in the
redundant mode, programming the first 256 bytes also will program the last 256 bytes with the same data.
Programming the EEPROM in the non-redundant mode is recommended. Program the data to both
locations before entering redundant mode.
Follow this procedure to program a byte of EEPROM:
1. Clear EERAS1 and EERAS0 and set EELAT in the EECTL. Set value of t_EEPGM. (See notes a
and b.)
2. Write the desired data to any user EEPROM address.
3. Set the EEPGM bit. (See note c.)
4. Wait for a time, t_EEPGM, to program the byte.
MC68HC908AT32 Data Sheet, Rev. 3.1
Freescale Semiconductor
57