CYW20737
1.11 Peripheral Transport Unit
1.11.1 Broadcom Serial Communications Interface
The CYW20737 provides a 2-pin master BSC interface, which can be used to retrieve configuration information from an external
EEPROM or to communicate with peripherals such as track-ball or touch-pad modules, and motion tracking ICs used in mouse
devices. The BSC interface is compatible with I2C slave devices. The BSC does not support multimaster capability or flexible wait-
state insertion by either master or slave devices.
The following transfer clock rates are supported by the BSC:
■ 100 kHz
■ 400 kHz
■ 800 kHz (not a standard I2C-compatible speed.)
■ 1 MHz (Compatibility with high-speed I2C-compatible devices is not guaranteed.)
The following transfer types are supported by the BSC:
■ Read (Up to 16 bytes can be read.)
■ Write (Up to 16 bytes can be written.)
■ Read-then-Write (Up to 16 bytes can be read and up to 16 bytes can be written.)
■ Write-then-Read (Up to 16 bytes can be written and up to 16 bytes can be read.)
Hardware controls the transfers, requiring minimal firmware setup and supervision.
The clock pin (SCL) and data pin (SDA) are both open-drain I/O pins. Pull-up resistors external to the CYW20737 are required on
both the SCL and SDA pins for proper operation.
1.11.2 UART Interface
The UART is a standard 2-wire interface (RX and TX) and has adjustable baud rates from 9600 bps to 1.5 kbps. The baud rate can
be selected via a vendor-specific UART HCI command. The interface supports the Bluetooth 3.0 UART HCI (H4) specification. The
default baud rate for H4 is 115.2 kbaud.
Both high and low baud rates can be supported by running the UART clock at 24 MHz.
The CYW20737 UART operates correctly with the host UART as long as the combined baud rate error of the two devices is within ±5%.
1.12 Clock Frequencies
The CYW20737 is set with crystal frequency of 24 MHz.
1.12.1 Crystal Oscillator
The crystal oscillator requires a crystal with an accuracy of ±20 ppm as defined by the Bluetooth specification. Two external load
capacitors in the range of 5 pF to 30 pF (see Figure 6) are required to work with the crystal oscillator. The selection of the load
capacitors is crystal-dependent. Table 6 shows the recommended crystal specifications.
Figure 6. Recommended Oscillator Configuration—12 pF Load Crystal
22 pF
XIN
Crystal
XOUT
20 pF
Table 6 shows the recommended crystal specifications.
Document Number: 002-16365 Rev. *C
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