BCM89359 Advance Data Sheet
UART Interface
UART Interface
The BCM89359 UART is a standard 4-wire interface (RX, TX, RTS, and 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 may be selected through a vendor-specific UART HCI command.
UART has a 1040-byte receive FIFO and a 1040-byte transmit FIFO to support EDR. Access to the FIFOs is
conducted through the AHB interface through either DMA or the CPU. The UART supports the Bluetooth 4.1
UART HCI specification: H4, a custom Extended H4, and H5. The default baud rate is 115.2 Kbaud.
The UART supports the 3-wire H5 UART transport, as described in the Bluetooth specification (“Three-wire
UART Transport Layer”). Compared to H4, the H5 UART transport reduces the number of signal lines required
by eliminating the CTS and RTS signals.
The BCM89359 UART can perform XON/XOFF flow control and includes hardware support for the Serial Line
Input Protocol (SLIP). It can also perform wake-on activity. For example, activity on the RX or CTS inputs can
wake the chip from a sleep state.
Normally, the UART baud rate is set by a configuration record downloaded after device reset, or by automatic
baud rate detection, and the host does not need to adjust the baud rate. Support for changing the baud rate
during normal HCI UART operation is included through a vendor-specific command that allows the host to adjust
the contents of the baud rate registers. The BCM89359 UARTs operate correctly with the host UART as long as
the combined baud rate error of the two devices is within ±2%.
Table 13: Example of Common Baud Rates
Desired Rate
Actual Rate
Error (%)
4000000
3692000
3000000
2000000
1500000
1444444
921600
460800
230400
115200
57600
4000000
3692308
3000000
2000000
1500000
1454544
923077
461538
230796
115385
57692
0.00
0.01
0.00
0.00
0.00
0.70
0.16
0.16
0.17
0.16
0.16
0.00
0.16
0.00
0.16
0.00
38400
38400
28800
28846
19200
19200
14400
14423
9600
9600
Broadcom®
September 9, 2014 • 89359-DS100-R
Page 50
BROADCOM CONFIDENTIAL
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