Teensy 4.1 with four AST-CAN485 boards

Development Boards Teensy
1

Hello,

I am planning to control four RS-485 devices using four UART ports on a Teensy 4.1 in combination with four AST-CAN485 boards. I intend to use the Arduino IDE and power the setup via USB (5V/3.3V). I wanted to inquire if there are any potential compatibility issues or considerations I should be aware of with this combination. Additionally, on the AST-CAN485 boards, I only require the RS-485 differential lines (A and B). I will use an external power supply to power the RS-485 devices.

Teensy 4.1 can only provide 3.3V logic levels, will this cause an issue with the MAX13487E transceiver on the AST-CAN485 boards? If so, would four SP3485 RS-485 boards be a better alternative?

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This is a bit out of my expertise, but I threw the scenario to Claude and it has some good advice, I believe. I edited a bit but here’s the gist:

1. MAX13487E logic levels (asymmetric problem)

  • DI/RE/SHDN (Teensy → transceiver): fine at 3.3V, TTL-compatible inputs, no shifting needed.
  • RO (transceiver → Teensy RX): swings to VCC = 5V since the board runs at 5V. Teensy 4.1 pins are not 5V tolerant (unlike Teensy 3.x), so this will damage the pin/MCU. Needs a level shifter or divider on RO only.

2. Bigger issue: AST-CAN485 isn’t a bare transceiver
It’s a full board with an onboard AT90CAN128 whose UART1 is hardwired to the MAX13487E’s DI/RO — those same pins are also broken out at header pins 22/23. So you can’t cleanly grab “just A/B” — the AT90CAN128 sits in that signal path unless you desolder it or tri-state its UART. Alternative is programming each board as a UART-to-RS485 bridge via the FTDI header, but that just moves the 5V/3.3V mismatch to the AT90CAN128 side instead.

3. SP3485 boards: yes, better fit
Native 3.3V, RO swings 0–3.3V, connects straight to Teensy 4.1 with no level shifting. Tradeoff: no AutoDirection, so you drive DE/RE manually (one GPIO per port). This is trivial given Teensy 4.1’s 8 UARTs and spare GPIOs. Also avoids the “extra MCU in the path” problem entirely since it’s just a transceiver, not a dev board.

Other notes: common ground between Teensy/transceiver side and the RS-485 devices’ external supply, and standard termination/biasing per segment as needed. Baud rate isn’t a differentiator (both parts handle typical Modbus-range rates fine).

So, in summary…go with the SP3485 RS-485 :slight_smile: