MC68HC908AS32A Datasheet, PDF (56/280 Pages) Freescale Semiconductor, Inc – Microcontrollers

Memory
In order to avoid program disturbs, the row must be erased before any byte on that row is programmed.
1. Set the PGM bit. This configures the memory for program operation and enables the latching of
address and data for programming.
2. Read the FLASH block protect register.
3. Write any data to any FLASH location within the address range desired.
4. Wait for a time, t_NVS (minimum 10 µs).
5. Set the HVEN bit.
6. Wait for a time, t_PGS (minimum 5 µs).
7. Write data to the FLASH address being programmed⁽¹⁾.
8. Wait for time, t_PROG (minimum 30 µs).
9. Repeat step 7 and 8 until all desired bytes within the row are programmed.
10. Clear the PGM bit⁽¹⁾.
11. Wait for time, t_NVH (minimum 5 µs).
12. Clear the HVEN bit.
13. After time, t_RCV (typical 1 µs), the memory can be accessed in read mode again.
The FLASH programming algorithm flowchart is shown in Figure 2-14.
NOTE
A. Programming and erasing of FLASH locations can not be performed by
code being executed from the same FLASH array.
B. While these operations must be performed in the order shown, other
unrelated operations may occur between the steps. However, care must be
taken to ensure that these operations do not access any address within the
FLASH array memory space such as the COP control register at $FFFF.
C. It is highly recommended that interrupts be disabled during
program/erase operations.
D. Do not exceed t _PROG maximum or t_HV maximum. t_HV is defined as the
cumulative high voltage programming time to the same row before next
erase. t_HV must satisfy this condition: t_NVS+ t_NVH + t_PGS + (t_PROGX 64) ≤ t_HV
max. Please also see 19.11.3 FLASH Memory Characteristics.
E. The time between each FLASH address change (step 7 to step 7), or the
time between the last FLASH address programmed to clearing the PGM bit
(step 7 to step 10) must not exceed t_PROG maximum.
F. Be cautious when programming the FLASH array to ensure that
non-FLASH locations are not used as the address that is written to when
selecting either the desired row address range in step 3 of the algorithm or
the byte to be programmed in step 7 of the algorithm. This applies
particularly to $FFDA–$FFFF (38 bytes)
1. The time between each FLASH address change, or the time between the last FLASH address programmed to clearing PGM
bit, must not exceed the maximum programming time, t_PROG maximum.
MC68HC908AS32A Data Sheet, Rev. 2.0
56
Freescale Semiconductor