BQ76952EVM + MSP430F5529 BMS Firmware

Firmware for the BQ76952EVM using an MSP430F5529 as the I²C host. This project is based on TI’s BQ769x2 demo framework and adds higher-level helpers for:

• n-cell configuration using VCellMode
• periodic measurement polling and alarm handling
• CHG/DSG FET control from two GPIO inputs (P3.3 and P3.4)
• structured output in human-readable or JSON notification format in Hydrogen Style

---

Hardware

• MSP430F5529LP eval board (for programming over SBW)
• MSP430F5529 (host MCU)
• BQ76952EVM (battery monitor + protection + balancing)
• I²C: UCB1 mapped to P4.4=SCL, P4.5=SDA
• UART: UCA1 mapped to P4.2=RX, P4.3=TX
• FET control inputs:
  • P3.3 → enable Discharge (DSG)
  • P3.4 → enable Charge (CHG)
  • Both are configured as GPIO inputs with pulldown resistors

---

Build / Run

This code is intended to be built in PIO toolchain using the MSP430F5529 eval board for SBW programming.

At startup, main():

1. Stops the watchdog
2. Initializes GPIO, port mapping, UART, I²C
3. Resets the BQ76952
4. Applies RAM configuration via BQ769x2_Init()
5. Enables FET control and disables sleep for full-speed measurement updates
6. Enters the main polling loop

---

Configuration

Cell Count

This project is configured for 3 cells using VCellMode:

#define NUM_CELLS 3
#define NUM_CELLS_BITS 0x0007   // enable Cell1..Cell3

NUM_CELLS_BITS is written to the VCellMode register inside BQ769x2_Init().

---

Output Modes

A global output_mode controls whether telemetry is printed as:

• OUTPUT_HUMAN: readable console logs via printf
• OUTPUT_JSON: JSON notification packets (Hydrogen-style wrapper)

Select mode:

set_output_mode(OUTPUT_HUMAN);
// or
set_output_mode(OUTPUT_JSON);

JSON Wrapper

JSON output is wrapped in a common “notification” envelope via:

• send_json_notification_data(method, id, data_str)
• send_json_notification_fmt(method, id, data_fmt, ...)

All BMS-specific output functions ultimately route through these.

---

Key High-Level BQ76952 Functions

BQ769x2_Init()

Applies the core BQ76952 RAM configuration:

• enters CONFIG_UPDATE
• sets power / regulator / TS pin config
• sets VCellMode for your pack (3S by default)
• enables protections (SCD/OCD/OV/UV/etc.)
• sets alarm mask, balancing config, thresholds
• exits CONFIG_UPDATE

Used in main() once after reset, before enabling FETs.

---

BQ769x2_ReadAlarmStatus()

Reads AlarmStatus (direct command) and returns a 16-bit bitmask.

In main() this is used as the “scheduler”:

• if FULLSCAN bit is set → new measurements are ready
• if SafetyStatus alarm bits set → fetch safety status

---

BQ769x2_ReadAllVoltages()

Updates:

• CellVoltage[0..15] from Cell1Voltage..Cell16Voltage
• Stack_Voltage from StackVoltage
• Pack_Voltage from PACKPinVoltage
• LD_Voltage from LDPinVoltage

Important note: on the EVM, Pack_Voltage is the PACK pin after the FETs, so it may read ~0V when DSG/CHG FETs are open. Important note: on the EVM, Stack_Voltage is what we would usually call the "Battery Pack" voltage. Basically the voltage from top cell to GND.

---

BQ769x2_ReadVoltage(command)

Generic “direct command” voltage read:

• Cell voltages are returned in mV
• Stack/Pack/LD voltages are treated as 0.01V units and converted to mV

---

BQ769x2_ReadCurrent()

Reads CC2Current (direct command) and returns the raw 16-bit value.

Current direction: CC2 current is signed (two’s complement).

Recommended usage in this codebase:

int16_t current_mA = (int16_t)BQ769x2_ReadCurrent();
// positive = charging, negative = discharging

---

BQ769x2_ReadTemperature(command)

Reads a temperature direct command (e.g., TS1Temperature) and converts to °C:

Temperature_C = 0.1 * raw_K - 273.15

---

Protection / Fault Monitoring

BQ769x2_ReadSafetyStatus()

Reads:

• SafetyStatusA
• SafetyStatusB
• SafetyStatusC

And derives high-level flags:

• UV_Fault, OV_Fault, SCD_Fault, OCD_Fault
• ProtectionsTriggered

In main(), safety status is checked whenever AlarmStatus indicates safety-related bits or when a protection was previously active.

---

BQ769x2_ReadPFStatus()

Reads Permanent Failure status registers A/B/C. Useful when diagnosing “fuse LED” or persistent shutdown behavior.

---

FET Control (CHG/DSG)

BQ769x2_ReadFETStatus()

Reads FETStatus and updates globals:

• CHG, DSG, PCHG, PDSG

Use this to confirm the actual driver states.

---

BQ769x2_WriteFETStatus(bool DSG, bool CHG)

Controls CHG/DSG using the FET_CONTROL subcommand.

This function uses the BQ76952 convention:

• writing DSG_OFF=1 forces DSG OFF
• writing CHG_OFF=1 forces CHG OFF

So the function takes enable booleans and internally writes the “OFF” bits as needed.

Example:

BQ769x2_WriteFETStatus(true, false);  // DSG enabled, CHG forced off

Note: this is host control. The BQ76952 may still keep FETs open if protections are active (UV/OV/OCD/SCD/PF).

---

update_fets_from_buttons()

Reads the two GPIO inputs and applies FET control:

• P3.3 high → enable discharge (DSG)
• P3.4 high → enable charge (CHG)

Then:

BQ769x2_WriteFETStatus(dsg_enable, chg_enable);

This is called periodically from main() (currently every 20 cycles).

---

Output Helpers (Human + JSON)

These functions produce either console output or JSON notifications depending on output_mode.

output_bms_config(battery_type, cell_count)

Emits a config packet at startup and periodically.

output_bms_voltages(pack_mV, CellVoltage[], cell_count)

Emits pack + per-cell voltages.

output_fet_status(chg, dsg)

Emits CHG/DSG states as booleans/ints.

output_current_value(current_mA)

Emits signed current in mA.

---

Main Loop Behavior (Current Program)

The while(1) loop does:

1. Read AlarmStatus
2. If FULLSCAN complete → read voltages/current/temps → clear FULLSCAN bit
3. If safety alarm bits present → read safety status → clear alarm bits
4. Every ~20 cycles:
   • output voltages
   • update FETs from button inputs
   • read and output FET states
   • read and output current
5. Every ~100 cycles:
   • re-emit config and print faults if present
6. Delay ~20 ms

---

How to Write Your Own main()

A minimal, clean template:

int main(void)
{
    WDTCTL = WDTPW | WDTHOLD;

    GPIO_initPins();
    map_I2C_and_UART();
    UART_Init();
    I2C_initModule();

    set_output_mode(OUTPUT_JSON);

    CommandSubcommands(BQ769x2_RESET);
    delayUS(60000);

    BQ769x2_Init();
    delayUS(10000);

    CommandSubcommands(FET_ENABLE);
    CommandSubcommands(SLEEP_DISABLE);

    while (1)
    {
        uint16_t alarms = BQ769x2_ReadAlarmStatus();

        if (alarms & 0x80) {
            BQ769x2_ReadAllVoltages();
            int16_t current_mA = (int16_t)BQ769x2_ReadCurrent();

            // clear FULLSCAN complete bit
            DirectCommands(AlarmStatus, 0x0080, W);

            output_bms_voltages(Stack_Voltage, CellVoltage, NUM_CELLS);
            output_current_value(current_mA);
        }

        update_fets_from_buttons();

        if (alarms & 0xC000) {
            BQ769x2_ReadSafetyStatus();
            // clear safety alarm bits
            DirectCommands(AlarmStatus, 0xF800, W);
        }

        delayUS(20000);
    }
}

Recommended approach:

• Drive logic from AlarmStatus FULLSCAN rather than reading constantly.
• Keep FET control separate (e.g., button read each loop).
• Treat CC2 current as signed (cast to int16_t).

---

Common Gotchas

• PACK pin voltage reading 0V is normal if the PACK node is not being driven and/or FETs are open.
• Current is signed; treat CC2Current as two’s-complement.
• Protections (UV/OV/OCD/SCD/PF) can override host FET commands.
• If the EVM “FUSE” LED is on, check PF status and PF-related configuration.

---

Module Notes

• BQ769x2Header.h: contains direct command IDs, subcommands, and RAM register addresses
• Low-level comms:
  • I2C_ReadReg(), I2C_WriteReg(), ISR state machine
  • DirectCommands(), Subcommands(), CommandSubcommands()