MEC1632 datasheet(103/636 Pages) MICROCHIP

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DS00001592B-page 103

MEC1632

7.4.6

32 KHZ CLOCK DOMAIN SWITCHING

Clock sources for the 32K Clock Domain are illustrated in Figure 7-7 includes both an internal 32.768 KHz Silicon Oscil-

lator, 32.768 KHz Crystal Oscillator and an external 32 KHz clock source. 32 KHz Clock Domain Switching is con-

trolled as defined in Table 7-9.

The external 32 KHz clock source is configured using the EXT32K_VBAT bit D0 in the Clock Enable Register.

Note 7-7

The internal 32kHz Clock Source must first be enabled via the Clock Enable Register before

switching to the External 32kHz clock source either in the Forced mode (external only) or the auto-

switch mode.

Note 7-8

32K_EN is bit D1 in the Clock Enable Register.

Note 7-9

AD_EN is bit D2 in the Clock Enable Register.

Note 7-10

XTL32K_EN is bit D3 in the Clock Enable Register.

Note 7-11

XTL_SEL is bit D4 in the Clock Enable Register.

Note 7-12

If AD_EN is asserted (‘1’), the external 32 KHz Oscillator is selected and the external 32 KHz clock

stops (i.e., stays high or low for longer than ~31

s), the external clock must remain stopped for a

minimum of 300

s.

If AD_EN is asserted (‘1’), and the 32K_EN changes from asserted (‘1’) to de-asserted, AD_EN must

remain asserted for a minimum of 300

s.

At least one of 32K_EN or XTL32K_EN must be set to ‘1’ when switching AD_EN from ‘0’ to ‘1’ in

order for clock domain switching to take place. Once the 32K domain is switched, 32K_EN or

XTL32K_EN can be set to ‘0’.

Note 7-13

The

32.768 KHz Crystal Oscillator can be driven by a crystal or an external 32 KHz single-ended

clock source as defined by the XOSEL bit in the Clock Enable Register.

TABLE 7-9:

32KHZ CLOCK DOMAIN CONTROL

XTL_SEL

(

Note 7-11)

XTL32K_EN

(

Note 7-10)

AD_EN

(

Note 7-9)

32K_EN

(

Note 7-8)

Mode

(

Note 7-7)

Description

Notes

Off

32 KHz clocking (inter-

nal/external) disabled

(default)

Internal

Internal 32.768 KHz Silicon

Oscillator only

Internal

Internal 32.768 KHz Crystal

Oscillator only

Note 7-13

External

External 32 KHz input

(32KHZ_IN pin) only

Note 7-12

Auto Switch

Internal 32 KHz clock

source used only if external

not detected.

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