WT21-A-HCI Ver la hoja de datos (PDF) - Unspecified

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WT21-A-HCI

BLUETOOTH HCI MODULE

Unspecified 

4

Clock Generation

WT21 uses an internal 26 MHz crystal as a Bluetooth reference clock. All WT21 internal digital

clocks are generated using a phase locked loop, which is locked to the 26 MHz reference clock.

Also supplied to the digits is a watchdog clock, for use in low power modes. This uses a

frequency of 32.768kHz from CLK_32K, or an internally generated reference clock frequency of

1kHz, determined by PSKEY_DEEP_SLEEP_EXTERNAL_CLOCK_SOURCE.

The use of the watchdog clock is determined with respect to Bluetooth operation in low power

modes.

26 MHz

Bluetooth Radio

CLK_32kHz

AIO[0]

Watchdog clock

PLL

Digits

1 kHz

Figure 4: Clock Architecture

4.1

32kHz External Reference Clock

A

32kHz

clock

can

be

applied

to

CLK_32K,

using

PSKEY_DEEP_SLEEP_EXTERNAL_CLOCK_SOURCE.

The CLK_32K pad is in the VDD_PADS domain with all the other digital I/O pads and is driven

between levels specified in Section 11.3.4.

Bluegiga Technologies Oy

Page 17 of 56

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