Pin Mapping & Peripheral Config

Pin Mapping

Pin	Function	Peripheral	Description
PA0	ADC+	ADC1_IN1	Gas sensor positive (differential)
PA1	ADC−	ADC1_IN2	Gas sensor negative
PA2	DAC MSB	GPIO Output	AD5545 midscale/zero-scale select
PA3	DAC RS	GPIO Output	AD5545 reset (active low)
PA4	DAC LDAC	GPIO Output	AD5545 latch (pulse low to update)
PA5	SPI SCK	SPI1	DAC clock
PA6	SPI CS	GPIO Output	DAC chip select (active low)
PA7	SPI MOSI	SPI1	DAC data
PA8	LED	GPIO Output	Heartbeat (500 ms toggle)
PA9	UART TX	USART1	Host → sensor commands
PA10	UART RX	USART1	Sensor → host responses
PB7	I2C SDA	I2C1	SHT45 temperature/humidity sensor
PB8	I2C SCL	I2C1	SHT45 clock

Clock Tree

HSI (16 MHz)
  → PREDIV ÷4  →  4 MHz
  → PLL ×85    →  340 MHz
  → DIVR ÷2    →  SYSCLK = 170 MHz
                      │
                      ├── APB1 = 42.5 MHz  (I2C1, USART1)
                      └── APB2 = 85 MHz    (SPI1, ADC1)

Peripheral Configuration

ADC1 — Gas Sensor Input

Parameter	Value
Mode	Differential (PA0⁺ / PA1⁻)
Resolution	12-bit (0 – 4095 codes)
Sample time	6.5 cycles
Oversampling	8× hardware (ratio=3, shift=4)
Clock source	SYSCLK (170 MHz via `Adcsel::SYS`)
VREFINT cal.	On boot — actual VDD calculated

With 8× hardware oversampling the noise floor is effectively reduced by ~√8 ≈ 2.8, giving an effective resolution of ~13.5 bits. The hardware right-shifts the result back to 12-bit output, so ADC_MAX_CODE = 4095.

SPI1 — AD5545 DAC

Parameter	Value
Frequency	5 MHz
Mode	Mode 0 (CPOL=0, CPHA=0)
Data order	MSB first
Direction	TX only
Bus sharing	RTIC `ArbiterDevice`

USART1 — Host Communication

Parameter	Value
Baud rate	115200
Format	8N1
DMA	CH1 RX, CH2 TX

I2C1 — SHT45 Sensor

Parameter	Value
Frequency	100 kHz
Address	0x44 (SHT45)
DMA	CH4 RX, CH6 TX

DMA Channel Assignments

Channel	Peripheral	Direction
DMA1_CH1	USART1 RX	Peripheral → RAM
DMA1_CH2	USART1 TX	RAM → Peripheral
DMA1_CH3	SPI1 TX	RAM → Peripheral
DMA1_CH4	I2C1 RX	Peripheral → RAM
DMA1_CH5	ADC1	(Allocated, unused)
DMA1_CH6	I2C1 TX	RAM → Peripheral