Figure 1. BGP3 UART 5V to 3.3V translation

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1 BG ROBOTICS BGP3 Robotics Platform Documentation Document Number: Document Title: Author: BGP3-EN-001 BGP3 Controller Board Communications Protocol Wira Revision History: INITIAL VERSION UPDATED VERSION ADDED INFORMATION ON FIELD EEPROM UPDATE 1. OVERVIEW The BGP3 controller board communicates with external systems through a UART port (designated as UART1 in the schematics and the board layout). This port operates at 5V with 9600 baud rate, 8 data bits, no parity bit, and 1 stop bit. To accommodate communication with 3.3V systems, a Schottky diode is placed between the BGP3 microcontroller transmit pin and the 3.3V system receive pin. The 3.3V RX pin is pulled high to the 3.3V system power supply rail when the BGP3 TX pin is transmitting a logic high. BGP3 does not provide a 3.3V rail. Figure 1 shows the schematic used for this voltage translation. The BGP3 microcontroller RX pin will read a 3.3V input as logic high, thus a voltage translator is not needed to transmit a 3.3V UART signal to the board. Figure 1. BGP3 UART 5V to 3.3V translation Data communicated through the port is byte-oriented: a byte of data encapsulates a complete command that the controller board will interpret and execute if it is valid. BGP3 only transmits serial data when commanded as described in the next section, it will not send any data otherwise. BGP3 has a reception timeout of 2 seconds. If no UART packet has been received for 2 seconds, the board will turn off the motors and turn on the Loss-of- Signal indicator. Reception of a UART packet (valid or otherwise) resets the Loss-of-Signal timer and turns off the Loss-of-Signal indicator. 1

2 2. DATA PACKETS All data packets are 1-byte long. Data packets with the MSB being 1 are motor commands (check with 0x80 mask). Other commands to the BGP3 controller board are printable ASCII characters. 2.1 MOTOR COMMANDS Motor commands are encoded as follows: 1 2 Motor Select[0] Direction[1:0] Magnitude[3:0] Motor Select is a one bit value that denotes the motor to command. A value of 0 2 will drive the LEFT motor and a value of 1 2 will drive the RIGHT motor. The mask 0x40 can be used to isolate this bit. Direction is a two bit value that denotes which direction the motor should go. A value of 00 2 denotes a FORWARD direction, a value of 10 2 denotes a REVERSE direction. The values 01 2 and 11 2 are RESERVED. Current version of the BGP3 firmware (1.0) treats these reserved values as FORWARD except for the data packet 0xFF to improve reception reliability. The mask 0x30 can be used to isolate the direction bit(s). Magnitude is a four bit value that denotes the power that should be delivered to the motor. For example, a value of is stop, and a value of is full power. 0xFF is always ignored by the controller (use 0xCF for full forward right motor command). The mask 0x0F can be used to isolate the magnitude bits. 2.2 NON-MOTOR COMMANDS The following are valid commands for the BGP3 controller board. All the commands are encoded as ASCII characters. Command ASCII Hex Description Poll p 0x70 Sending the 'p' character to the controller board will result in the controller sending back its sampled analog sensor values and a magic byte. Upon the reception of the 'p' character, BGP3 will send back the following 1-byte values in order: SENSE_BATT1 (motor/servo battery) SENSE_FWD_L SENSE_FWD_S SENSE_LEFT SENSE_RIGHT SENSE_BATT0 (main battery) SENSE_OPTO 0xDD Release brake 0 0x30 Clears F_BRAKE flag. Resume accepting motor commands Set brake 1 0x31 Engage brake (sets F_BRAKE flag). Motors will be immediately stopped and further motor commands will be ignored until the brake flag is cleared 2

3 Enable optocoupler 2 0x32 Turn on optocoupler output Disable optocoupler 3 0x33 Turn off optocoupler output Restore actuator positions 4 0x34 Set actuators to latched values (O_ACTUATOR0 and O_ACTUATOR1 are written with previously latched positions). If no positions have been saved yet, it will be set to position 3 (1.5 ms) Save actuator positions 5 0x35 Save current actuators' positions Enable auto-stop 6 0x36 Engage forward auto-stop if robot is too close to something in the front (sets F_SENSOR_AID) Disable auto-stop 7 0x37 Disengage forward auto-stop (clears F_SENSOR_AID) Control actuator 0 w 0x77 Switch active control to actuator 0 Control actuator 1 e 0x65 Switch active control to actuator 1 Set actuator to position 0 a 0x61 Set currently active actuator to position 0 Set actuator to position 1 s 0x73 Set currently active actuator to position 1 Set actuator to position 2 d 0x64 Set currently active actuator to position 2 Set actuator to position 3 f 0x66 Set currently active actuator to position 3 (1.5 ms) Set actuator to position 4 g 0x67 Set currently active actuator to position 4 Set actuator to position 5 h 0x68 Set currently active actuator to position 5 Set actuator to position 6 j 0x6A Set currently active actuator to position 6 Analog motor control z 0x7A Drive motors based on the analog values of the left and right sensors Direct motor control c 0x63 Drive motors' PWM signal directly from left and right input voltages UART motor control x 0x78 Default motor control mode (UART) Shutdown Mode * 0x2A Indicate shutdown (slowly blinking status light) and ignore further commands until reset EEPROM Reprogram r 0x72 See section 3 (firmware version 1.1 only) 3

4 3. EEPROM PROGRAMMING (FIRMWARE VERSION 1.1 OR LATER) Some configuration of the BGP3 controller board is stored in EEPROM. This configuration can be updated over UART, which allows adjustment of the board's operation without having to reprogram the microcontroller. To enter the EEPROM programming mode, the user must send the character 'r' three times. Other data packets in between will break the sequence. If no 'r' character is received within 4 seconds of another, the process will time out and the sequence will need to be restarted. If the user has successfully entered programming mode, low battery 0 status indicator will be turned steady-on (no matter what the battery voltage is). The user must then send the address and the value to write to the EEPROM. Both low battery indicators will be on after an address has been received. If the user failed to provide a value within 4 seconds of entering the address, the process will time out and no new value will be written to the EEPROM. If the process is successful, the new value will take effect immediately (actuator commands must be re-sent since the values are latched). Make sure to not poll the robot when this process is underway because the polling packet will be interpreted as a valid address or value. Interrupts are globally disabled after the reception of the value byte. The interrupts will be re-enabled after the write is completed. The controller will not be able to receive UART packets during the period where interrupts are disabled. A delay between programming sequences is required to ensure that no UART packets are dropped. No UART packets will be dropped if the delay is at least 100 ms since the value byte was sent. Lower delays may be possible, but do so at your own risk. 'r' 'r' 'r' EEPROM address EEPROM value B0 LED on B0 and B1 LEDs on Command sequence to program the EEPROM through UART. All fields are 1-byte. Data packets received between the 'r' characters will break the sequence. After the third 'r' packet, the next two received values will be interpreted as the address and the new EEPROM value Below are the configuration fields that can be updated through this process: Address Function Description hex dec Servo position 0-6 duty cycle Integer from 0 to 250 denoting the duty cycle of the servo signal at position 0 to 6 (8 μs resolution, 0 to 2 ms) Unused E 8-14 Servo position 0-6 overflow duty cycle 0F 15 - Unused - Integer from 0 to 250 denoting the overflow duty cycle of the servo signal at position 0 to 6. This is used if the servo signal is between 2 ms to 4 ms. The 0 to 2 ms duty cycle must be set to at least 249, otherwise this overflow is not used! Battery warning cutoff Integer value for the low battery warning threshold Formula: value = [warning voltage] / 10 * Battery critical cutoff Integer value for the low battery critical threshold Formula: value = [critical voltage] / 10 * Auto-stop sensor threshold Integer value for front sensor auto-stop threshold 4

5 13 19 Active braking 0 for no active braking, 1-15 for power level Running average N Size of smoothing buffer size for calculating running average of the sensor values Timeout Loss of signal timeout in multiples of 20 ms. The default is 100 for 2 seconds. 5