19.4
Programming and Erasing Flash Memory
The H8/3434F’s on-chip flash memory is programmed and erased by software, using the CPU.
The flash memory can operate in program mode, erase mode, program-verify mode, erase-verify
mode, or prewrite-verify mode. Transitions to these modes can be made by setting the P, E, PV,
and EV bits in the flash memory control register (FLMCR).
The flash memory cannot be read while being programmed or erased. The program that controls
the programming and erasing of the flash memory must be stored and executed in on-chip RAM or
in external memory. A description of each mode is given below, with recommended flowcharts
and sample programs for programming and erasing.
For details on programming and erasing, refer to section 19.7, Flash Memory Programming and
Erasing Precautions.
19.4.1 Program Mode
To write data into the flash memory, follow the programming algorithm shown in figure 19.8. This
programming algorithm can write data without subjecting the device to voltage stress or impairing
the reliability of programmed data.
To program data, first specify the area to be written in flash memory with erase block registers
EBR1 and EBR2, then write the data to the address to be programmed, as in writing to RAM. The
flash memory latches the address and data in an address latch and data latch. Next set the P bit in
FLMCR, selecting program mode. The programming duration is the time during which the P bit is
set. A software timer should be used to provide a programming duration of about 10 to 20 µs. The
value of N, the number of attempts, should be set so that the total programming time does not
exceed 1 ms. Programming for too long a time, due to program runaway for example, can cause
device damage. Before selecting program mode, set up the watchdog timer so as to prevent
overprogramming.
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HITACHI [ HITACHI SEMICONDUCTOR ]
