I2C Peripheral Addresses and Bus Configuration for DAC5578 and ADS7830 in PLFM RADAR Firmware

DAC5578 DACs use I²C bus hi2c1 with addresses 0x48 and 0x49, while ADS7830 ADCs use hi2c2 with addresses 0x48, 0x49, 0x4A, or 0x4B depending on hardware pin-strapping.

The PLFM RADAR project uses a STM32F7 microcontroller to manage multiple analog peripherals through separate I²C buses. Understanding the I2C peripheral addresses and bus configuration for DAC5578 and ADS7830 devices is essential for modifying the firmware or debugging communication issues. This article breaks down the exact addresses, HAL handles, and initialization code found in the open-source firmware.

I2C Bus Assignment Strategy

The firmware deliberately separates DAC and ADC devices across two I²C peripherals to eliminate bus contention and match the PCB routing.

Peripheral	I²C Bus (HAL Handle)	Purpose
DAC5578 (2× devices)	hi2c1	Gate voltage (Vg) control for power amplifier channels
ADS7830 (3× devices)	hi2c2	Idq measurement and thermal monitoring

This separation allows simultaneous transactions without arbitration delays and simplifies timing requirements for the 8-channel DAC updates.

DAC5578 I2C Configuration

Each DAC5578 is an 8-channel, 8-bit digital-to-analog converter. The PLFM RADAR Main Board contains two instances for independent PA channel control.

Default I²C Addresses

Device	Address	PCB Reference	Handle Name
First DAC5578	0x48	U7	hdac1
Second DAC5578	0x49	U69	hdac2

Initialization Code

In main.cpp (lines 1845-1855), both DACs are initialized with &hi2c1 and their respective addresses:

#include "DAC5578.H"

DAC5578_HandleTypeDef hdac1, hdac2;

/* Initialize first DAC5578 at 0x48 */
bool ok1 = DAC5578_Init(&hdac1, &hi2c1, 0x48, 8,
                        GPIOB, DAC5578_LDAC_PIN, 
                        GPIOB, DAC5578_CLR_PIN);

/* Initialize second DAC5578 at 0x49 */
bool ok2 = DAC5578_Init(&hdac2, &hi2c1, 0x49, 8,
                        GPIOB, DAC5578_LDAC_PIN, 
                        GPIOB, DAC5578_CLR_PIN);

The DAC5578_Init() function signature confirms:

• Bus: hi2c1 pointer (first STM32 I²C peripheral)
• Resolution: Fixed at 8 bits (resolution = 8)
• Control pins: LDAC and CLR on GPIOB

Post-Initialization Setup

After successful init, the code configures both devices for synchronized updates:

/* Clear all outputs to zero scale */
DAC5578_SetClearCode(&hdac1, DAC5578_CLR_CODE_ZERO);
DAC5578_SetClearCode(&hdac2, DAC5578_CLR_CODE_ZERO);

/* Enable LDAC broadcast for all 8 channels */
DAC5578_SetupLDAC(&hdac1, 0xFF);
DAC5578_SetupLDAC(&hdac2, 0xFF);

ADS7830 I2C Configuration

The ADS7830 is an 8-channel, 8-bit analog-to-digital converter with address-selectable I²C operation. The PLFM RADAR firmware addresses three instances across two functional domains.

Address Selection via Pin Strapping

The ADS7830 datasheet (and ADS7830.H) defines four possible addresses based on the ADDR pin connection:

ADDR Pin Connection	I²C Address
GND	0x48
VDD	0x49
SDA	0x4A
SCL	0x4B

Deployed Instances

Function	Address	PCB Reference	Handle Name	Lines in main.cpp
Idq measurement (ch 0-7)	0x48	U88	hadc1	1900-1909
Idq measurement (ch 0-7)	0x4A	U89	hadc2	1910-1919
Thermal monitoring	0x49	U10	hadc3	1990-1999

ADC Initialization Code

All three instances use &hi2c2 (the second STM32 I²C peripheral):

#include "ADS7830.H"

ADS7830_HandleTypeDef hadc1, hadc2, hadc3;

/* Idq ADC #1: ADDR = GND → 0x48 */
bool okA = ADS7830_Init(&hadc1, &hi2c2, 0x48,
                        ADS7830_SDMODE_SINGLE, 
                        ADS7830_PDIRON_ADON);

/* Idq ADC #2: ADDR = SDA → 0x4A */
bool okB = ADS7830_Init(&hadc2, &hi2c2, 0x4A,
                        ADS7830_SDMODE_SINGLE, 
                        ADS7830_PDIRON_ADON);

/* Thermal monitor: ADDR = VDD → 0x49 */
bool okC = ADS7830_Init(&hadc3, &hi2c2, 0x49,
                        ADS7830_SDMODE_SINGLE, 
                        ADS7830_PDIRON_ADON);

The ADS7830_SDMODE_SINGLE parameter configures single-ended measurements; the driver also supports differential mode via ADS7830_SDMODE_DIFF.

Reading ADC Channels

/* Read channel 3 from Idq ADC #1 */
uint8_t raw_value = ADS7830_Measure_SingleEnded(&hadc1, 3);

/* Convert TMP37 thermal sensor reading to temperature */
float temperature_c = raw_value * 0.64705f;  // 165°C / 255 LSB

Key Source Files

File	Path	Purpose
DAC5578.H	9_Firmware/9_1_Microcontroller/9_1_1_C_Cpp_Libraries/DAC5578.H	Handle struct, API prototypes, command constants
DAC5578.c	9_Firmware/9_1_Microcontroller/9_1_1_C_Cpp_Libraries/DAC5578.c	I²C write/read implementation, power modes
ADS7830.H	9_Firmware/9_1_Microcontroller/9_1_1_C_Cpp_Libraries/ADS7830.H	Address constants, measurement mode enums
ADS7830.c	9_Firmware/9_1_Microcontroller/9_1_1_C_Cpp_Libraries/ADS7830.c	I²C command sequencing, conversion timing
main.cpp	9_Firmware/9_1_Microcontroller/9_1_3_C_Cpp_Code/main.cpp	System startup, peripheral instantiation

Common Configuration Issues and Solutions

Address Collision on Shared Bus

The DAC5578 at 0x48 and 0x49 and the ADS7830 at 0x48/0x49 would conflict if placed on the same bus. The separate hi2c1/hi2c2 assignment prevents this.

Verifying Bus Communication

Both drivers return boolean status from *_Init(). The firmware checks these and logs via DIAG macros:

if (!ok1) {
    DIAG_ERROR("DAC5578 @ 0x48 initialization failed");
}

Modifying Addresses for Custom Boards

To change an ADS7830 address:

1. Physically restrap the ADDR pin (GND, VDD, SDA, or SCL)
2. Update the address constant in main.cpp initialization call
3. No driver modification needed—the ADS7830.H already defines all four options

Summary

• DAC5578 devices connect to hi2c1 at addresses 0x48 and 0x49 for gate voltage control
• ADS7830 devices connect to hi2c2 at addresses 0x48, 0x4A, and 0x49 (selected by pin strapping) for current and temperature sensing
• Initialization occurs in main.cpp lines 1845-1855 (DACs) and 1900-1999 (ADCs)
• The separate bus architecture eliminates address conflicts despite overlapping address ranges

Frequently Asked Questions

What I2C addresses can the ADS7830 support?

The ADS7830 supports four addresses based on the ADDR pin strapping: 0x48 (GND), 0x49 (VDD), 0x4A (SDA), and 0x4B (SCL). The PLFM RADAR firmware uses 0x48, 0x4A for Idq measurement and 0x49 for thermal monitoring. These are hardware-determined and cannot be changed via software.

Why are DAC and ADC devices on separate I2C buses?

The DAC5578 and ADS7830 both use addresses in the 0x48-0x49 range. Placing them on separate buses (hi2c1 and hi2c2) prevents address collisions. This design also isolates the DAC's real-time gate voltage updates from the ADC's sampling operations, improving timing determinism.

How do I add a fourth ADS7830 to the system?

Strap the new device's ADDR pin to SCL to select address 0x4B (unused in the current design). Add a new ADS7830_HandleTypeDef declaration, then call ADS7830_Init() with &hi2c2 and 0x4B. Ensure your PCB routing connects the device to the second I²C peripheral's SDA/SCL lines.

{
  "mcpServers": {
    "instagit": {
      "command": "npx",
      "args": ["-y", "instagit@latest"]
    }
  }
}