User's Manual

BT860
Datasheet
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8.2. UART Interface
The BT860 shares a single UART for Bluetooth. The UART is a standard four-wire interface (RX, TX, RTS, and CTS)
with adjustable baud rates from 38400 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 1040-byte transmits FIFO to support EDR. Access to the FIFO is
conducted through the AHB interface through either DMA or the CPU. The UART supports the Bluetooth 4.2
UART HCI specification: H4, and a custom Extended H4. The default baud rate is 115.2 Kbaud.
The BT860 UART can perform XON/XOFF flow control and includes hardware support for Serial Line Input
Protocol (SLIP). It can also perform wake-on activity. For the BT860 is supported BT to wake-up Host.
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 BT860 UARTs operate correctly with the host UART if the combined
baud rate error of the two devices is within ±2%.
Table 9: Example of common baud rates
Desired Rate Actual Rate Error (%)
4000000 4000000 0.00
3000000 3000000 0.00
2000000 2000000 0.00
1500000 1500000 0.00
921600 923077 0.16
460800 461538 0.16
230400 230796 0.17
115200 115385 0.16
57600 57692 0.16
38400 38400 0.00
8.2.1. Simultaneous UART Transport and Bridging
The BT860 supports UART or USB interfaces that can function as the host controller interface (HCI). Typically, a
customer application would choose one of the two interfaces and the other would be idle. The BT860 allows the
UART transport to operate simultaneously with the USB. To operate this way, the assumption is that the USB
would function as the primary host transport, while the UART would function as a secondary communication
channel that can operate at the same time. This can enable the following applications -
 Bridging primary HCI transport traffic to another device via the UART
 Generic communication to an external device for a vendor-supported application via the UART
Table 10 and Figure 2 shows UART timing of specifications.