STM32H563 Peripheral Saturation – Moving to Multi-MCU (Stepper + DC Load Slaves) – Architecture Review

[Prathapraj]

Hello ST Community,

I am working on a commercial vending machine controller and would like to get feedback from ST engineers and experienced STM32 designers regarding a system architecture change.

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Problem Statement

Our current system uses a single MCU, but we are now hitting hard peripheral limits, mainly:

• Timer availability (stepper + DC motor control)

• GPIO interrupt count

• GPIO pin availability

• Increasing real-time jitter when multiple loads are active

This is not a software optimization issue anymore; it is a resource saturation issue.

Because of this, we are planning to move from a single-MCU architecture to a multi-MCU system.

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Proposed Architecture

• Master MCU: STM32H563ZIT6

  • Handles:

    • All sensors (ADC / digital)

    • Control logic & state machine

    • Recipe execution

    • Safety checks

    • UI communication

  • No direct motor timing generation

• Slave MCUs (2x):

  • Dedicated load-handling controllers

  • One for stepper motors

  • One for DC motors / PWM-based loads

  • Slaves perform only deterministic actuation

  • No sensors, no business logic

• Inter-MCU Communication:

  • Considering CAN (FDCAN) as primary bus

  • RS485 as an alternative / secondary option

I have attached a block-level architecture diagram for reference.

Current Peripheral Usage on STM32H563 (New Approach)

Peripheral Instances Used Usage

ADC	1	12 channels
I2C	I2C1, I2C2, I2C3	3
TIM	TIM1, TIM2, TIM3, TIM4, TIM5, TIM8	6
UART / USART	USART1, USART2, USART3, UART5, UART7, UART8, UART9, UART12	8
DAC	DAC1	1
GPIO Interrupts	–	14
GPIO Inputs	–	20
GPIO Outputs	–	5
CAN	FDCAN1	1

Even with this split, the master MCU is still heavily utilized, which is why motor timing is fully offloaded to slave MCUs.

Questions for Discussion

1. Is this master + load-slave MCU split the correct long-term approach for vending machine / appliance-class products?

2. From an STM32 architectural perspective, are there recommended design patterns for timer- and interrupt-heavy motor systems?

3. CAN vs RS485 for multi-MCU control:

   • CAN seems preferable for arbitration and fault handling

   • Any STM32H5-specific considerations?

4. Are there common pitfalls (boot sequence, synchronization, fault recovery, debugging) that should be addressed early?

5. From a product lifetime standpoint (8–10 years), does this architecture look robust and maintainable?

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I would appreciate feedback from:

• ST application engineers

• Developers with multi-MCU STM32 designs

• Anyone with experience in CAN-based industrial / appliance systems

Thank you in advance for your insights.

Best regards,
Prathapraj S,

Boatload Minds Pvt Ltd.

@stm32h5,can,motor-control,system-architecture,multi-mcu