RN4870 MCU Interface

Figure 1 shows the power scheme using a 3.3 V low-dropout regulator to the RN4870 and a host MCU. This scheme ensures the same voltage for both the module and the MCU. Also shown here are the basic Universal Asynchronous Receiver Transmitter (UART) connections to the host MCU and the GPIO for control and indication.

Figure 1

Figure 2 shows the recommended connections for running the RN4870/71 on a coin cell battery.

Figure 2

As we can see from Figure 2 (Note 2), the GPIO pins of the RN4870 are configurable. They can be configured to different functions using the ASCII command interface.

Pin Default Function
P07 Low Battery
P10 Status 2
P11 Status 1
P22 None
P24 None
P31 RSSI Indication
P32 Link Drop
P33 UART RX Indication
P34 Pairing
P35 None
P12 None
P13 None
Low Battery Indication
Pin output goes low when the battery level is below a specified level. To set the battery level, EEPROM settings need to be changed.
Status 1
This indication pin is used along with the Status 2 pin to indicate the current status of the module. Refer to the table below for details of the status indication.
Status 2
This indication pin is used along with the Status 1 pin to indicate the current status of the module. Refer to the table below for details of the status indication.
RSSI Indication
This pin is used to indicate the quality of the link based on the RSSI level. If the RSSI level is lower than the specified values, then the RSSI indication pin goes low. The threshold for the RSSI link quality can be set in EEPROM.
Link Drop
This pin can used to force the module to drop the current BLE link with a peer device. Pulling the Link Drop pin low will force the disconnect. The pin needs to be pulled low for at least 10 ms.
UART RX Indication
This enables the UART Low-Power mode. To enter Low-Power mode, the pin is pulled low and the UART RX is activated for receiving data.
Pairing Key
This pin can be used to force the module to enter Standby mode. The pin needs to be pulled down for at least 160 ms.
RF Active Indication
This indication pin is used to indicate that the module is currently having an active transmission and receiving of BLE data
Status 1 Status 2 State
High High Power On/Shutdown
High Low Standby state
Low Low Connection established
Low High Data session open
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