Silicon Labs

Page 10 of 35

3.1 I/O Ports

3.1.1 I/O Configurations

Each I/O port can be configured as an input or output. When configured as input, each I/O port can also be

configured with internal pull-up, pull-down or tri-state. Pull-down or pull-up can only be configured to whole

port, not individual pins. Unused I/O pins should have defined level and not be floating. See the BLE

Configuration Guide for more information about the configuration.

During reset the I/O pins are configured as inputs with pull-ups.

Note: Pins configured as peripheral I/O signals do not have pull-up / -down capability

3.1.2 Rese

rved I/O’s

The high current driving pins P1_0 and P1_1 are reserved for the internal RF front end control. These pins are

not exposed in BLE121LR and they can’t be used for application purposes.

P1_7 is also used for the RF front end control but as an output it can be used to control the external DCDC for

lowering the peak current drawn from the battery

. The function of P1_7 can’t be altered. If external DCD is not

used then P1_7 should be left not connected.

3.2 UART

UART baud rate can be configured up 2 Mbps. See the BLE Configuration Guide for more information.

Following table lists commonly used baud rates for BLE121LR

Baud rate (bps)

Error (%)

2400

0.14

4800

0.14

9600

0.14

14 400

0.03

19 200

0.14

28 800

0.03

38 400

0.14

57 600

0.03

76 800

0.14

115 200

0.03

230 400

0.03

Table 5: Commonly used baud rates for BLE121LR