BCM20707 Datasheet, PDF (19/65 Pages) Cypress Semiconductor – Complies with Bluetooth Core Specification version 4.2 including BR/EDR/BLE

BCM20707 Preliminary Data Sheet
Peripheral Transport Unit
UART Interface
The UART physical interface is a standard, 4-wire interface (RX, TX, RTS, and CTS) with adjustable baud rates
from 38400 bps to 6 Mbps. During initial boot, UART speeds may be limited to 750 kbps. The baud rate may be
selected via a vendor-specific UART HCI command. The BCM20707 has a 1040-byte receive FIFO and a 1040-
byte transmit FIFO to support enhanced data rates. The interface supports the Bluetooth UART HCI (H4)
specification. The default baud rate for H4 is 115.2 kbaud.
The UART clock default setting is 24 MHz, and can be configured to run as high as 48 MHz to support up to
6 Mbps. The baud rate of the BCM20707 UART is controlled by two values. The first is a UART clock divisor
(set in the DLBR register) that divides the UART clock by an integer multiple of 16. The second is a baud rate
adjustment (set in the DHBR register) that is used to specify a number of UART clock cycles to stuff in the first
or second half of each bit time. Up to eight UART cycles can be inserted into the first half of each bit time, and
up to eight UART clock cycles can be inserted into the end of each bit time.
Table 1 contains example values to generate common baud rates with a 24 MHz UART clock.
Baud Rate (bps)
6M
4M
3M
2M
1M
921600
460800
230400
115200
57600
38400
Table 1: Common Baud Rate Examples, 24 MHz Clock
Baud Rate Adjustment
High Nibble
Low Nibble
0xFF
0xFF
0xFF
0XFF
0X44
0x05
0x02
0x04
0x00
0x00
0x01
0xF8
0xF4
0xF8
0XF4
0XFF
0x05
0x02
0x04
0x00
0x00
0x00
Mode
High rate
High rate
High rate
High rate
Normal
Normal
Normal
Normal
Normal
Normal
Normal
Error (%)
0.00
0.00
0.00
0.00
0.00
0.16
0.16
0.16
0.16
0.16
0.00
Table 2 contains example values to generate common baud rates with a 48 MHz UART clock.
Broadcom^®
May 27, 2016 • 20707-DS206-R
BROADCOM CONFIDENTIAL
Bluetooth SoC
Page 18