MOTOROLA
3-6
ON-CHIP MEMORY
MC68HC11A8
TECHNICAL DATA
3
The erased state of an EEPROM byte is $FF. Programming changes ones to zeros. If
any bit in a location needs to be changed from a zero to a one, the byte must be erased
in a separate operation before it is reprogrammed. If a new data byte has no ones in
bit positions which were already programmed to zero, it is acceptable to program the
new data without erasing the EEPROM byte first. For example, programming $50 to a
location which was already $55 would change the location to $50.
Programming and erasure of the EEPROM relies on an internal high-voltage charge
pump. At E clock frequencies below 2 MHz the efficiency of this charge pump decreas-
es which increases the time required to program or erase a location. The recommend-
ed program and erase time is 10 milliseconds when the E clock is 2 MHz and should
be increased to as much as 20 milliseconds when E is between 1 MHz and 2 MHz.
When the E clock is below 1 MHz, the clock source for the charge pump should be
switched from the system clock to an on-chip R-C oscillator clock. This is done by set-
ting the CSEL bit in the OPTION register. A 10 millisecond period should be allowed
after setting the CSEL bit to allow the charge pump to stabilize. Note that the CSEL bit
also controls a clock to the analog-to-digital converter subsystem.
3.5.1 EEPROM Programming Control Register (PPROG)
This 8-bit register is used to control programming and erasure of the 512-byte EE-
PROM. Reset clears this register so the EEPROM is configured for normal reads.
ODD — Program Odd Rows (TEST)
EVEN — Program Even Rows (TEST)
Bit 5 — Not implemented.
This bit always reads zero.
BYTE — Byte Erase Select
This bit overrides the ROW bit.
0 = Row or Bulk Erase
1 = Erase Only One Byte
ROW — Row Erase Select
If the BYTE bit is 1, ROW has no meaning.
0 = Bulk Erase
1 = Row Erase
ERASE — Erase Mode Select
0 = Normal Read or Program
1 = Erase Mode
7
6
5
0
0
4
3
2
1
0
$
1
03B
RESET
ODD
0
EVEN
0
BYTE
0
ROW
0
ERASE
0
EELAT
0
EEPGM
0
PPROG