AN1827 Freescale Semiconductor / Motorola, AN1827 Datasheet - Page 10

• Manufacturer Part Number: AN1827
• Description: Programming and Erasing FLASH Memory on the MC68HC908AS60
• Manufacturer: Freescale Semiconductor / Motorola

Application Note
10
NOTE:
NOTE:
When FLASH memory is programmed/erased with the PLL on or in
monitor mode, bus frequency is not always the same as the external
clock frequency divided by four. Since the charge pump frequency is
derived from the bus frequency, confirm the bus frequency being used.
If the charge pump frequency is not between 1.8 MHz and 2.5 MHz,
Motorola does not guarantee the operation, electrical, or reliability
specifications of the FLASH.
The HVEN bit in the FLASH control register enables the charge pump to
generate high voltages for program and erase modes. The charge pump
also generates a regulated voltage for the margin read mode in the
smart programming algorithm. During programming, the HVEN bit
should be asserted only for 1 ms to 1.2 ms at a time. (See
Asserting HVEN for longer than 1.2 ms at a time risks program disturb,
where an erased bit on the same row becomes unintentionally
programmed. Program disturb is a common soft fault and can be
recovered by erasing the row and reprogramming using the smart
programming algorithm.
f
Table 1. Bus Frequency Divide Ratios for Charge Pump Clock
Freescale Semiconductor, Inc.
Bus
2.4576
4.9152
2.000
4.000
8.000
8.400
For More Information On This Product,
(MHz)
Go to: www.freescale.com
FDIV1
0
0
0
0
1
1
FDIV0
0
0
1
1
1
1
Division
1
1
2
2
4
4
Figure
f
Pump
MOTOROLA
2.4576
2.4576
2.000
2.000
2.000
2.100
(MHz)
AN1827
8.)