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Thread: Maximum serial port speed on Teensy 3.2?

  1. #1
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    Maximum serial port speed on Teensy 3.2?

    Teensy 3 has 3 serial ports. Serial1 connects to the USB port and I think I remember reading the specified baud in Serial1.begin(<baud>) doesn't actually matter because the Serial USB port transmits at USB speeds regardless. Correct me if I'm wrong though.

    But what I'm really after is the maximum speed I can use on Serial2 and Serial3. I have a Bluetooth module (emulating a serial port) connected to Serial2 and am wondering if it's possible to get closer to the 1Mbs Bluetooth rate than just 115200. I'd really have a need for more bandwidth.

  2. #2
    Senior Member+ Frank B's Avatar
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    It is 6MBs. USB is "Serial", Serial1..3 are Hardware. Serial1 has the largest FIFO, and preferrable for high speeds.

  3. #3
    Senior Member Epyon's Avatar
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    Serial connects to the USB port. Serial1, Serial2 and Serial3 are hardware UARTs that by default connect to pins 1/2, 9/10 and 7/8 respectively (TX/RX). The UART can run up to 115 Kbaud without a hitch, and even higher baud rates are possible. Some users here run them up to 2 Mbaud and above. I thought the theoretical maximum was 4.5 Mbaud.

    Be aware that only Serial1 and Serial2 have FIFOs. If you want to use UARTs at high speed, use these. Otherwise the interrupt rate can be so high that your application will not perform as expected and/or data loss will happen.

  4. #4
    Senior Member+ defragster's Avatar
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    I don't have T_3.0 - but elsewhere on T3.1 and onward::
    USB == Serial.begin( value ignored )
    # UART == Serial#.begin( declared baud rate and optional params )

    As far as actual usable baud rate: as FrankB notes 6Mbs can work on those UARTS with hardware FIFO, but 2-3Mbs seems to run better and be more stable.

    On T_3.1 and T_3.2 hardware FiFO is on Serial1 and Serial2, Serial3 doesn't have the FIFO and won't hit those speeds as well [ I know on the slower T_LC with no FIFO it maxes out somewhere over 200Kb ]

  5. #5
    Senior Member Constantin's Avatar
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    You also want to consider using RTS/CTS at high speeds, if possible. Teensy offers very easy ways to enable them, see https://www.pjrc.com/teensy/td_uart.html

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