
Operating Modes and On-Chip Memory
EEPROM
M68HC11E Family — Rev. 5
Data Sheet
MOTOROLA
Operating Modes and On-Chip Memory
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2.5  EEPROM 
Some E-series devices contain 512 bytes of on-chip EEPROM. The 
MC68HC811E2 contains 2048 bytes of EEPROM with selectable base address. All 
E-series devices contain the EEPROM-based CONFIG register.
2.5.1  EEPROM and CONFIG Programming and Erasure
The erased state of an EEPROM bit is 1. During a read operation, bit lines are 
precharged to 1. The floating gate devices of programmed bits conduct and pull the 
bit lines to 0. Unprogrammed bits remain at the precharged level and are read as 
ones. Programming a bit to 1 causes no change. Programming a bit to 0 changes 
the bit so that subsequent reads return 0. 
When appropriate bits in the BPROT register are cleared, the PPROG register 
controls programming and erasing the EEPROM. The PPROG register can be read 
or written at any time, but logic enforces defined programming and erasing 
sequences to prevent unintentional changes to EEPROM data. When the EELAT 
bit in the PPROG register is cleared, the EEPROM can be read as if it were a ROM. 
The on-chip charge pump that generates the EEPROM programming voltage from 
V
DD
 uses MOS capacitors, which are relatively small in value. The efficiency of this 
charge pump and its drive capability are affected by the level of V
DD
 and the 
frequency of the driving clock. The load depends on the number of bits being 
programmed or erased and capacitances in the EEPROM array. 
The clock source driving the charge pump is software selectable. When the clock 
select (CSEL) bit in the OPTION register is 0, the E clock is used; when CSEL is 1, 
an on-chip resistor-capacitor (RC) oscillator is used. 
The EEPROM programming voltage power supply voltage to the EEPROM array 
is not enabled until there has been a write to PPROG with EELAT set and PGM 
cleared. This must be followed by a write to a valid EEPROM location or to the 
CONFIG address, and then a write to PPROG with both the EELAT and EPGM bits 
set. Any attempt to set both EELAT and EPGM during the same write operation 
results in neither bit being set. 
2.5.1.1  Block Protect Register 
This register prevents inadvertent writes to both the CONFIG register and 
EEPROM. The active bits in this register are initialized to 1 out of reset and can be 
cleared only during the first 64 E-clock cycles after reset in the normal modes. 
When these bits are cleared, the associated EEPROM section and the CONFIG 
register can be programmed or erased. EEPROM is only visible if the EEON bit in 
the CONFIG register is set. The bits in the BPROT register can be written to 1 at 
any time to protect EEPROM and the CONFIG register. In test or bootstrap modes, 
write protection is inhibited and BPROT can be written repeatedly. Address ranges 
for protected areas of EEPROM differ significantly for the MC68HC811E2. Refer to 
Figure 2-16
. 
F
Freescale Semiconductor, Inc.
n
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