Data Sheet

Bluegiga – A Silicon Labs Company 16
5.2 UART
There is one UART port available on the BT121. By default it is used for BGAPI™ host interface but with
BGScript™ it can be used as an application UART. The UART supports all standard baud rates up to 4 Mbps.
RTS/CTS handshake scheme is supported and recommended for every application for reliable data transfer.
5.3 I
2
C
BT121 has up to two I
2
C ports available. Both support standard mode up to 100 kbps, fast modes up to 400
kbps and Fast Mode Plus with improved drive capability and clock stretching up to 1 Mbps.
5.4 SPI
BT121 has up to two SPI ports available. Both can be configured for frame sizes from 4 to 16 bits and clock
frequencies up to 18 MHz. Both ports provide internal CRC calculation. An optional slave select signal (NSS)
is provided for hardware assisted data strobing in applications requiring high bus throughputs.
5.5 ADC
BT121 contains a 4-channel 12-bit ADC with multiple external input sources as well as an internal battery
measurement and temperature measurement possibility. ADC input voltage range is 0 to VDD.
5.5.1 Accessory functions of the ADC
In addition to the external ADC inputs an internal temperature sensor or internal supply voltage divider can be
selected as the input to ADC.
Power supply range when using internal ADC functions is 2.4 to 3.6 VDC.
5.6 DAC
BT121 contains a 2-channel 12-bit DAC, with two independent outputs. DAC output voltage range is 0 to
VDD.
Power supply range when using internal DAC functions is 2.4 to 3.6 VDC.
5.7 Real-time clock
BT121 contains a real-time clock (RTC) with full calendar support and sub-second resolution. The RTC can be
used for periodic or specifically programmed wakeups. The RTC is clocked by an internal crystal oscillator
which is always on as long as power is supplied to the module.
5.8 Microcontroller programming interface
The preferred method of programming the BT121 is by using the Bluegiga DFU through the UART host
interface. A problem may occur if the DFU is disabled by disabling the UART or if the DFU is overwritten
accidentally. Then the DFU would need to be re-uploaded.
The two methods of firmware upload are through the SWDIO/SWCLK interface (PA13 and PA14) using an
ARM serial debug adapter, or by forcing the BOOT0 signal high and by resetting the module to make it boot
into a recovery mode. Then the BGTool software can be used to recover the DFU through the UART interface.