PRELIMINARY
CYW20710
5.2 HCI Transport Detection Configuration
The CYW20710 supports the following interface types for the HCI transport from the host:
■
■
UART (H4 and H5)
SPI
Only one host interface can be active at a time. The firmware performs a transport detect function at boot-time to determine which
host is the active transport. It can auto-detect the UART interface, but the SPI interface must be selected by strapping the SCL pin to 0.
The complete algorithm is summarized as follows:
1. Determine if SCL is pulled low. If it is, select SPI as HCI host transport.
2. Determine if any local NVRAM contains a valid configuration file. If it does and a transport configuration entry is present, select
the active transport according to entry, and then exit the transport detection routine.
3. Look for CTS_N = 0 on the UART interface. If it is present, select UART.
4. Repeat Step 3 until transport is determined.
5.3 UART Interface
The UART physical interface is a standard, 4-wire interface (RX, TX, RTS, CTS) with adjustable baud rates from 9600 bps to 4.0
Mbps. The interface features an automatic baud rate detection capability that returns a baud rate selection. Alternatively, the baud
rate can be selected via a vendor-specific UART HCI command. The interface supports Bluetooth UART HCI (H4) specifications. The
default baud rate for H4 is 115.2 Kbaud.
The following baud rates are supported:
9600
115200
230400
460800
921600
1444444
1500000
2000000
3000000
3250000
3692000
4000000
14400
19200
28800
38400
57600
Normally, the UART baud rate is set by a configuration record downloaded after reset or by automatic baud rate detection. The host
does not need to adjust the baud rate. Support for changing the baud rate during normal HCI UART operation is provided through a
vendor-specific command.
The CYW20710 UART operates with the host UART correctly, provided the combined baud rate error of the two devices is within ±2%.
5.3.1 HCI 3-Wire Transport (UART H5)
The CYW20710 supports H5 UART transport for serial UART communications. H5 reduces the number of signal lines required by
eliminating CTS and RTS, when compared to H4. In addition, in-band sleep signaling is supported over the same interface so that
the 4-wire UART and the 2-wire sleep signaling interface can be reduced to a 2-wire UART interface, saving four IOs on the host.
H5 requires the use of an external LPO. CTS must be pulled low.
Document No. 002-14804 Rev. *H
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