R8CSLASH20 datasheet(407/501 Pages) RENESAS

407 / 501 page

R8C/20 Group, R8C/21 Group

19. Flash Memory

Rev.2.00 Aug 27, 2008

Page 391 of 458

REJ09B0250-0200

Figure 19.11

Process to Reduce Power Consumption in High-Speed On-Chip Oscillator Mode,

Low-Speed On-Chip Oscillator Mode (XIN Clock Stops) and Low-Speed Clock Mode

(XIN Clock Stops)

Transfer a high-speed on-chip oscillator mode, low-

speed on-chip oscillator mode (XIN clock stops)

program to the RAM

Jump to the high-speed on-chip oscillator mode, low-

speed on-chip oscillator mode (XIN clock stops) program

which has been transferred to the RAM.

(The subsequent processing is executed by a program in

the RAM.)

Write 0 to the FMR01 bit before writing 1

(CPU rewrite mode enabled)

Switch the clock source for the CPU clock.

Turn XIN off

Process in high-speed on-chip oscillator

mode, low-speed on-chip oscillator mode

(XIN clock stops)

Write 0 to the FMR01 bit

(CPU rewrite mode disabled)

Jump to a specified address in the flash memory

High-speed on-chip oscillator

mode, low-speed on-chip

oscillator mode (XIN clock stops)

program

NOTES:

1. Set the FMR01 bit to 1 (CPU rewrite mode enabled) before setting the FMSTP bit to 1 .

2. Before the clock source for CPU clock can be changed, the clock to which to be changed must be stable.

3. Insert a 30

µs wait time in a program. Do not access to the flash memory during this wait time.

Write 1 to the FMSTP bit (Flash memory stops.

Low power consumption state)(1)

Wait until the flash memory circuit stabilizes

(30

µs)(3)

Write 0 to the FMSTP bit

(flash memory operation)

Turn XIN clock on

→wait until oscillation

stabilizes

→switch the clock source for CPU

clock(2)

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