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Bluetooth Peripheral Transport Unit

BCM4354 Data Sheet

BROADCOM CONFIDENTIAL

Broadcom®

October 15, 2014 • 4354-DS109-R

Page 44

Section 7: Bluetooth Peripheral Transport

Unit

SPI Interface

The BCM4354 supports a slave SPI HCI transport with an input clock range of up to 16 MHz. Higher clock rates

can be possible. The physical interface between the SPI master and the BCM4354 consists of the four SPI

signals (SPI_CSB, SPI_CLK, SPI_SI, and SPI_SO) and one interrupt signal (SPI_INT). The SPI signals are

muxed onto the UART signals, see Table 6. The BCM4354 can be configured to accept active-low or active-high

polarity on the SPI_CSB chip select signal. It can also be configured to drive an active-low or active-high

SPI_INT interrupt signal. Bit ordering on the SPI_SI and SPI_SO data lines can be configured as either little-

endian or big-endian. Additionally, proprietary sleep mode and half-duplex handshaking is implemented

between the SPI master and the BCM4354. The SPI_INT is required to negotiate the start of a transaction. The

SPI interface does not require flow control in the middle of a payload. The FIFO is large enough to handle the

largest packet size. Only the SPI master can stop the flow of bytes on the data lines, since it controls SPI_CSB

and SPI_CLK. Flow control should be implemented in the higher layer protocols.

SPI/UART Transport Detection

The BT_HOST_WAKE (BT_GPIO1) pin is also used for BT transport detection. The transport detection occurs

during the power-up sequence. It selects either UART or SPI transport operation based on the following pin

state:

• If the BT_HOST_WAKE (BT_GPIO1) pin is pulled low by an external pull-down during power-up, it selects

the SPI transport interface.

• If the BT_HOST_WAKE (BT_GPIO1) pin is not pulled low externally during power-up, then the default

internal pull-up is detected as a high and it selects the UART transport interface.

Table 6: SPI to UART Signal Mapping

SPI Signals

UART Signals

SPI_CLK

UART_CTS_N

SPI_CSB

UART_RTS_N

SPI_MISO

UART_TXD

SPI_MOSI

UART_RXD

SPI_INT

BT_DEV_WAKE

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