Datasheet

EEPROM
MC68HC908AB32 — Rev. 1.1 Technical Data
Freescale Semiconductor EEPROM
75
5.9.1 EEPROM Programming
The unprogrammed or erased state of an EEPROM bit is a logic 1.
Programming changes the state to a logic 0. Only EEPROM bytes in the
non-protected blocks and the EENVR register can be programmed.
Use the following procedure to program a byte of EEPROM:
1. Clear EERAS1 and EERAS0, and set EELAT in the EECR.
(A)
2. Write the desired data to the desired EEPROM address.
(B)
3. Set the EEPGM bit.
(C)
Go to step 7 if AUTO is set.
4. Wait for a time, t
EEPGM
, to program the byte.
5. Clear EEPGM bit.
6. Wait for a time, t
EEFPV
, for the programming voltage to fall.
Go to step 8.
7. Poll the EEPGM bit until it is cleared by the internal timer.
(D)
8. Clear EELAT bit.
(E)
NOTE: A. EERAS1 and EERAS0 must be cleared for programming. Setting the
EELAT bit configures the address and data buses to latch data for
programming the array. Only data with a valid EEPROM address will be
latched. If EELAT is set, other writes to the EECR will be allowed after a
valid EEPROM write.
B. If more than one valid EEPROM writes occur, the last address and
data will be latched, overriding the previous address and data. Once
written data to the desired address, do not read EEPROM locations
other than the written location. (Reading an EEPROM location returns
the latched data, and causes the read address to be latched.)
C. The EEPGM bit cannot be set if the EELAT bit is cleared or a non-
valid EEPROM address is latched. This is to ensure proper
programming sequence. Once EEPGM is set, do not read any EEPROM
locations, otherwise the current program cycle will be unsuccessful.
When EEPGM is set, the on-board programming sequence will be
activated.