TMP86FS49FG datasheet(29/42 Pages) TOSHIBA

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Page 27

TMP86FS49FG

2.2.4.4 SLOW mode

SLOW mode is controlled by the system control register 2 (SYSCR2).

The following is the methods to switch the mode with the warm-up counter (TC4, TC3).

(1) Switching from NORMAL2 mode to SLOW1 mode

First, set SYSCK (Bit5 in SYSCR2) to switch the main system clock to the low-frequency clock

for SLOW2 mode.

Next, clear XEN (Bit7 in SYSCR2) to turn off high-frequency oscillation.

Note: The high-frequency clock can be continued oscillation in order to return to NORMAL2 mode from

SLOW mode quickly. Always turn off oscillation of high-frequency clock when switching from

SLOW mode to stop mode.

When the low-frequency clock oscillation is unstable, wait until oscillation stabilizes before per-

forming the above operations. The timer/counter 6, 5, 4, 3 (TC6, TC5, TC4, TC3) can conveniently

be used to confirm that low-frequency clock oscillation has stabilized.

(2) Switching from SLOW1 mode to NORMAL2 mode

First, set XEN (Bit7 in SYSCR2) to turn on the high-frequency oscillation. When time for stabili-

zation (Warm up) has been taken by the timer/counter 4, 3 (TC4, TC3), clear SYSCK (Bit5 in

SYSCR2) to switch the main system clock to the high-frequency clock.

Example 1 :Switching from NORMAL2 mode to SLOW1 mode.

SET

(SYSCR2). 5

; SYSCR2<SYSCK>

← 1

(Switches the main system clock to the low-frequency

clock for SLOW2)

CLR

(SYSCR2). 7

; SYSCR2<XEN>

← 0

(Turns off high-frequency oscillation)

Example 2 :Switching to the SLOW1 mode after low-frequency clock has stabilized.

SET

(SYSCR2). 6

; SYSCR2<XTEN>

← 1

(TC3CR), 43H

; Sets mode for TC4, TC3 (16-bit TC, fs for source)

(TC4CR), 05H

LDW

(TTREG3), 8000H

; Sets warm-up time (Depend on oscillator accompanied)

; IMF

← 0

SET

(EIRH). 1

; Enables INTTC4

; IMF

← 1

SET

(TC4CR). 3

; Starts TC4, 3

PINTTC4:

CLR

(TC4CR). 3

; Stops TC4, 3

SET

(SYSCR2). 5

; SYSCR2<SYSCK>

← 1

(Switches the main system clock to the low-frequency clock)

CLR

(SYSCR2). 7

; SYSCR2<XEN>

← 0

(Turns off high-frequency oscillation)

RETI

VINTTC4:

PINTTC4

; INTTC4 vector table

TENTATIVE

TMP86FS49FG Datasheet(PDF) 29 Page - Toshiba Semiconductor

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