STA2500D datasheet(27/57 Pages) STMICROELECTRONICS

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STA2500D

General specification

Doc ID 16067 Rev 1

27/57

6.5

System clock

The STA2500D works with a sine wave or digital clock provided on the BT_REF_CLK_IN

pin. Detailed specifications are found in Section 2.4.

6.6

Low power clock

The low power clock is used by the Bluetooth Controller as reference clock during the low

power modes. It requires an accuracy of +250 ppm. The STA2500D requires a digital clock

to be provided on the BT_LP_CLK pin, with frequencies of 3.2 kHz, 32 kHz and 32.768 kHz.

After power-up, the low power clock must be available before the reset is released. It must

remain active all the time until the STA2500D is powered off.

6.7

Clock detection

An integrated automatic detection algorithm detects the system and low power clock

frequencies after a hardware reset. The steps in the clock detection routine are:

●

Identification of the system clock frequency (9.6 MHz, 10 MHz, 13 MHz, 16 MHz,

16.8MHz, 19.2 MHz, 26 MHz, 33.6 MHz or 38.4 MHz)

●

Identification of the low power clock (3.2 kHz, 32.768 kHz or 32 kHz).

6.8

Clock request signals

To allow minimum power consumption, a clock request feature is available so that the

system clock (BT_REF_CLK_IN) can be stopped when not needed by the Bluetooth

system. The clock request signal can be active high or active low, and the STA2500D

supports internal propagation of clock request signal coming from another device in the

system.

Different configurations as described below are supported immediately after reset and in all

Bluetooth operation modes, provided that BT_VIO_A is available.

The clock request functionality is based on four different signals: BT_CLK_REQ_OUT_1,

BT_CLK_REQ_OUT_2, BT_CLK_REQ_IN_1, BT_CLK_REQ_IN_2, with the following

function:

●

BT_CLK_REQ_OUT_1: active low or high clock request, depending on HW

configuration pins (Table ). Support for either push-pull or open drain output.

●

BT_CLK_REQ_OUT_2: active low clock request, only used in combination with SPI

mode. Support for either push-pull or open drain output.

●

BT_CLK_REQ_IN_1: active high clock request input from an other device, depending

on HW configuration pin.

●

BT_CLK_REQ_IN_2: active low clock request input from an other device.

The following modes are supported:

●

Active high clock request input and output combined with UART or SPI:

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