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Thread: Teensy 4.1 - Fourth I2C device?

  1. #1
    Junior Member
    Join Date
    Nov 2012

    Teensy 4.1 - Fourth I2C device?

    I'm wondering, doesn't the processor have four I2C controllers? Why are only 3 available?

  2. #2
    Senior Member+ Frank B's Avatar
    Join Date
    Apr 2014
    Because the pins are needed for other things.

    Usually I2C chips support different adresses, so for most applications three busses are enough.

    Other things are important, too.

  3. #3
    Senior Member PaulStoffregen's Avatar
    Join Date
    Nov 2012
    Not all of the chip's pins can come to the outside pins on Teensy. Some are connected to the ethernet and flash chips on the PCB. Some aren't connected to anything at all, only because it's not physically feasible to bring out more pins.

    Many difficult trade-off decisions were made about which pins to bring out, especially in the early days leading up to Teensy 4.0. For example, at earlier beta version with the 1052 chip has 8 all serial ports. When we switched to the 1062 which brought a 3rd CAN peripheral, and the only one supporting the higher speed CAN-FD, the decision was made that CAN-FD was more important on Teensy 4.0 than having an 8th serial port.

    Similar decisions were made with Teensy 4.1. The pins we did bring to the edge of the PCB were considered to be the most important features. Access to the 4th I2C port was thought to be less important than the extra analog inputs and having access to a continuous set of 16 pins within one of the native 32 bit port registers.

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