Sorry if this has been asked before.
It looks like the focus is more on using protocols etc. rather than messing about with pins directly, almost like a computer. This is like when we lost the parallel port.
Thank you.
Your pal,
PAAUX4
Well only Paul can answer about the tradeoffs, but others can speculate on the answers (bear in mind, my answers are just idle speculation).
I would imagine the main issue is cost. Larger boards cost more to make. The more expensive a board is, the fewer customers will buy it if they don't need all of the features. I suspect for many people the $20 price is a sweet spot for ordering multiple Teensys vs. only one. In addition to just the size of the PCB, you have the additional complexity of routing all of those signals from the chip to the board. IIRC, the Teensy 3.0, 3.1, and 3.2 all used 4 layer boards, while the 3.5, 3.6, and 4.0 used 6 layer boards. Paul has said cramming all of the routing for those 6 layers took an enormous amount of work.
With some of the parts (notably the SD and USB pins), you can have signal reliability problems if the entire wire length is too long.
As somebody who puts boards into costumes and such (or at least plans out such things, even if I don't always finish things), I find the Teensy LC/3.2/4.0 to fit in better than the Teensy 3.5/3.6 in small spaces. For example when using a breadboard, I can use the cheap 170 pin breadboards to hold the Teensy 3.2/4.0, while for the 3.5/3.6, I have to use the longer 300 pin 1/2 size breadboards.
Also, somewhat unrelated:
- What is FlexIO?
- Are pins D- and D- under the USB port for the first or second USB port?
- What benefit does the power pin have over a hardware switch? Is it just the ability to use a momentary switch?
For FlexIO, you will need to do a deep dive into the datasheet.
I believe the D-/D+ pins are for the second USB port (i.e. not the connected to the micro USB socket used for programming the Teensy). Paul has said there were issues with signal strength and running at the full USB 2.x speeds that prevented the D-/D+ pins of the first USB connector from being brought out.
I believe this is just bringing out a pin on the chip that provides this functionality. If you want a hardware switch, you can always remove the solder jumper that connects VIN to VUSB and put the switch there.
Paul has said that he is looking at a larger layout similar to the 3.6 that brings out more pins for a Teensy 4.x follow-on.