BCM43455 Preliminary Data Sheet
Bluetooth Peripheral Transport Unit
Section 7: Bluetooth Peripheral Transport Unit
SPI Interface
The BCM43455 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 BCM43455 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 5). The BCM43455 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 BCM43455. 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.
Table 5: SPI-to-UART Signal Mapping
SPI Signals
UART Signals
SPI_CLK
SPI_CSB
SPI_MISO
SPI_MOSI
SPI_INT
BT_UART_CTS_N
BT_UART_RTS_N
BT_UART_RXD
BT_UART_TXD
BT_HOST_WAKE
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.
Broadcom®
November 5, 2015 • 43455-DS109-R
Page 47
BROADCOM CONFIDENTIAL
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