The BM71 provides a flexible MCU interface, which can be tailored to your specific needs. The most basic interface requires only two UART interface signals. Two additional control signals are also recommended: one to reset the module, the other to enable BM71 firmware/configuration programming.
The BM71 is configured and controlled via binary packet communications over a UART interface. The BLEDK3 Command Set Users Guide contains a complete command/event/response listing and details of the interface. Additionally, the module provides status indication/control via several programmable GPIO pins, simplifying MCU firmware and state-machine development.
Further documentation on the MCU interface and available GPIO pin functions may be found in the BM70/71 device data sheet, as well as the BLEDK3 release notes
"BLEDK3" refers to the name of the application firmware running in the BM71 module.
Binary Packet Communications
The MCU host sends specially formatted "Command" packets to the module. Depending on the command, the module will issue "Event" response packets and eventually a "Command Complete" response packet as shown:
Commands cover the following operational categories:
- Common (Reading basic device information)
- GAP Commands (BLE Connection Management)
- GATT Client (BLE Data Exchange)
- GATT Server (BLE Data Exchange)
- GATT Transparent
Please refer to the BLEDK3 Command Set Users Guide for complete details.
A checksum is used to test data integrity on command packets.
- Sign-extend to 16-bits, then add, all required bytes,
- Calculate the 2's complement on the lower 8-bits of the result
Response Packet ("Command Complete")
A checksum may be used to test data integrity on response packets.
- Sign-extend to 16-bits, then add, all required bytes (including the checksum byte),
- If there are no errors, the result will be 0xXX00
The following depicts a command/response sequence for the "Read Local Information" command:
Basic Interface (Manual Pattern Mode)
In the simplest configuration, the module requires two UART interface signals (TX & RX). Two additional control signals are also recommended: one to reset the module, the other to enable BM70 firmware/configuration programming:
The Reset input pin (RST_N) is used to Reset the BM70/71 with an active-low pulse with a minimum pulse width of 63 ns.
An internal pull-up is enabled on this input, however, an external pull-up resistor of 4.7 kOhm is recommended.
P2_0 (System Configuration)
This pin is used to enable module firmware/configuration updates:
P2_0 has an internal pull-up, enabling Application mode by default.
HCI_TXD / HCI_RXD
UART data output / input signals.
The default port configuration for the UART is described in the table below:
Basic Interface (Auto Pattern Mode)
The basic signal interface for Auto Pattern mode (Transparent UART) adds 2 active-low UART flow control signals, P3_6/UART_RTS and P0_0/UART_CTS:
Special Function Pins
Several additional programmable GPIO signals are available to be interfaced with the host MCU. Some of these are used for control, while others may be used to monitor module state as an alternative to UART event packets.
Some of these pin functions are dedicated, however, most can be re-programmed with the UI Configuration Tool.
P1_6 (UART_RX_IND Pin - Programmable)
When enabled, this active-low input pin function can be used to reduce the active current consumption of the module by disabling the UART HCI_RXD pin function. When enabled, the host MCU needs to insert a ~3mS delay before sending a command packet as shown:
P1_7 (PAIRING_KEY Pin - Programmable)
During an active BLE connection, this active-low input pin function can be used to force the module to terminate the link and enter into standby mode. This signal needs to be applied for at least 160mS as shown:
Px_x (LINK_DROP Pin - Programmable)
During an active BLE connection, this active-low input pin function can be used to force the module to terminate the link and enter into shutdown mode. This signal needs to be applied for at least 10mS as shown:
LINK_DROP pin function is not assigned to any pin by default. Assign to a pin using the UI Configuration Tool.
P0_2 (LED0 Pin - Dedicated)
This active-low output pin function can be used to signal various BLE connection states. Options are also provided to flash this output at various rates.
P2_7 (UART_TX_IND Pin - Dedicated)
This active-low output pin function can be used to signal the host MCU that data will be transmitted out of the HCI_TXD pin after a specific interval:
P1_3/P1_2 (STATUS2/STATUS1 Pins - Programmable)When enabled, these output pin functions indicate a variety module connection states, as shown in the following table:
|H||H||Shutdown Mode||BM70 is shutdown|
|H||L||Standby Mode||BM70 sends advertising packets and is discoverable and connectable|
|L||L||Connected Mode||BLE Link is established (BLE GATT Operating Mode)|
|L||H||Connected Mode||BLE Link is established (Transparent UART Service Operating Mode)|
Px_x (LOW_BATTERY_IND Pin - Programmable)
This active-low output pin function can be used to signal a low battery condition on VBAT. Additionally, the module can be configured to enter shutdown if the battery voltage remains low for a certain time interval.
LOW_BATTERY_IND pin functionality is not assigned to any pin by default. Assign it using the UI Configuration Tool.
Related UI Config Tool Parameters:
- Battery Detection Interval
- Low Battery Level
- Normal Battery Level
- Low-Battery-to-Shutdown Time
Px_x (RSSI_IND Pin - Programmable)
If enabled, this output pin function can be used to signal the BLE connection link quality. The module checks two link quality levels which can be configured using the UI Configuration Tool. If link quality is lower than "RSSI Weak Threshold", then RSSI_IND output is low. If link quality is higher than "RSSI Normal Threshold", then RSSI_IND output is high, as shown here:
RSSI_IND pin functionality is not assigned to any pin by default. Assign it using the UI Configuration Tool.
Related UI Configuration Tool Parameters:
- Link Quality Detection
- RSSI Normal Threshold
- RSSI Weak Threshold