pwm_node

Firmware for CAN-controlled PWM controller.

• PCB: pwm_node_pcb.

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Table of Contents

• pwm_node
  • 1 Overview
    • 1.1 Bill of Materials (BOM)
    • 1.2 Block Diagram
    • 1.3 Pin Configurations
    • 1.4 Clock Configurations
  • 2 TJA1051T/3 CAN Bus Transceiver
  • 3 PWM Breakouts
    • 3.1 Clocks
    • 3.2 Pulse Width Modulation (PWM) Timer
      • 3.2.1 Timer Calculations
    • 3.3 Direct Memory Access (DMA)

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1 Overview

1.1 Bill of Materials (BOM)

Manufacturer Part Number	Manufacturer	Description	Quantity	Notes
STM32L432KC	STMicroelectronics	32-bit MCU	1
TJA1051T/3	NXP USA Inc.	CAN Bus Transceiver	1

1.2 Block Diagram

Drawio file here: pwm_node.drawio.

1.3 Pin Configurations

CubeMX Pinout

Pin & Peripherals Table

STM32L432KC	Peripheral	Config	Connection	Notes
PB3	SYS_JTDO-SWO		TC2050 SWD Pin 6: SWO
PA14	SYS_JTCK-SWCLK		TC2050 SWD Pin 4: SWCLK
PA13	SYS_JTMS-SWDIO		TC2050 SWD Pin 2: SWDIO
PA11	CAN1_RX		TJA1051T/3 Pin 1: TXD
PA12	CAN1_TX		TJA1051T/3 Pin 4: RXD
PA5	TIM2_CH1	PWM Generation CH1	Breakout
PA1	TIM2_CH2	PWM Generation CH2	Breakout
PA2	TIM2_CH3	PWM Generation CH3	Breakout
PA3	TIM2_CH4	PWM Generation CH4	Breakout
PB7	USART1_RX		TBD
PB6	USART1_TX		TBD
PA9	I2C1_SCL		TBD
PA10	I2C1_SDA		TBD

1.4 Clock Configurations

8 MHz High Speed External (HSE)
↓
Phase-Locked Loop Main (PLLM)
↓
80 MHz SYSCLK
↓
80 MHz HCLK
↓
 → 80 MHz APB1 (Maxed) → 80 MHz APB1 Timer
 → 80 MHz APB2 (Maxed) → 80 MHz APB2 Timer

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2 TJA1051T/3 CAN Bus Transceiver

Carry over from nerve.

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3 PWM Breakouts

3.1 Clocks

APB2: 80 MHz (clock for TIM2 PWM output channels).

3.2 Pulse Width Modulation (PWM) Timer

3.2.1 Timer Calculations

Given the PWM equation:

$$f_{PWM} = \frac{f_{TIM}}{ \left( ARR + 1 \right) \times \left( PSC + 1 \right) }$$

• $f_{TIM} = 1 \space \mathrm{MHz}$
  • Choosing 1 MHz (1 µs per tick) to simplify calculations.
• $ARR = 20000 - 1$
  • Counter period, aka Auto Reload Register (ARR) of 19999 is used to simplify the translation of 1 ms and 2 ms pulse widths.
• $f_{PWM} = 1 \space \mathrm{MHz}$
  • Aiming for 1 µs ticks, or $1 \times 10 ^{-6} \space \mathrm{s}$.
  • Calculating for required PWM frequency:
    • $f_{PWM} = \frac{1}{1 \times 10 ^{-6} \space \mathrm{s}} = 1 \space \mathrm{MHz}$

Thus, the prescaler, $PSC = 80 - 1$.

With these settings the following PWM values can be obtained:

1 ms -> CCR = 1000
1.5 ms -> CCR = 1500
2 ms -> CCR = 2000

3.3 Direct Memory Access (DMA)

TIM2_UP DMA1 Stream2:

• Direction: Memory to Peripheral.
• Mode: Circular.
  • Application is PWM servos.
• Peripheral Increment Address: Disabled.
• Memory Increment Address: Enabled.
• (Both Peripheral and Memory) Data Width: Word.
• Use FIFO: Disabled.