Introduction
One of the biggest issues with MSXI's electrical system was its inconsistency in parts and pinouts. There were at least 3 variations of the CAN controller/transceiver circuit and which SPI bus they were connected to, making debugging difficult. Some used different footprints, while others used different parts. This also made inventory a challenge, as each board had its own very specific set of components.
To increase board consistency and ease debugging, we propose a controller board that consists of shared core components such as the microcontroller, CAN transceiver, and possibly some debug LEDs or IOs. These controller boards would likely use a mezzanine connector to allow breakouts to carrier boards, which should be much simpler.
Key Features
- Allows creation of a debug carrier board to allow self-test of the MCU and CAN
- Simplifies inventory management and software, allowing a single core config for all boards
- Simplifies board debugging - isolates issues to either the controller or carrier boards
- Reduces cost of bringing up backup boards
Part Selection
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STM32F072RBT6
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ARM Cortex-M0 microcontroller
Includes CAN controller, 51 IOs, 64-LQFP
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CAN Transceiver
Replacement for the SN65HVD232DR
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CAN connector
TODO: Move to different connector for internal CAN connections?
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TE 1565357-6
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50 pin, 0.5mm pitch, 4-6mm stack height
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10106813-051112LF
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Mezzostak Hermaphroditic connectors
Samples have been requested
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LS2-125-01-F-D-RA1
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Samtec LS2 locking hermaphroditic connectors
SICK SHIT, but they keep getting sold out on digikey and are a bit more expensive
Samples have been requested
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Peripheral Selection
- 37 GPIOs
- 2 SPI, 2 I2C, 4 USART, CAN, USB, HDMI-CEC
- 16 Channel 12-bit ADC
- 18 Capacitive Sense Channels
- 2 Analog Comparators
- Serial Wire Debug (SWD)
Most I/O pins on the STM32F072 are also used for peripheral functions such as SPI, I2C, USART, CAN, USB, CEC, SWD, etc. To increase flexibility, most of the I/O will be routed to the carrier board. Since the peripherals and I/O pins are muxed internally, the controller board can provide either function to the carrier board without special requirements.
Important notes
- PC13, PC14 and PC15 are supplied through the power switch. Since the switch only sinks a limited amount of current (3 mA), the use of GPIOs PC13 to PC15 in output mode is limited: The speed should not exceed 2 MHz with a maximum load of 30 pF. These GPIOs must not be used as current sources (e.g. to drive an LED).