Teensy4.1 special features + additional pins

[gndTeensy]

Hello!

I have a general question about the 55 I/O pins on the Teensy4.1. I see on the back of the board and pin layout that there are additional pins. But these pins look like they are for traced to specific modules like the SD card and QSPI memory. If I do not want to use these modules and just need extra I/O pins, can I just solder wires them and use them in the program like I would with the other I/O pins on the top side of the board?

Thank you!

[KurtE]

Yes you can use those other pins for GPIO stuff.

From my Excel document on T4.x I have the page:

Which shows those pins. are in these areas. For SD, at one point I made a simple plug in circuit board that broke those out. Sparkfun also sells some as well.

[Fluxanode]

Kurt, can you post a link to the spreadsheet? I must have an old version it doesn't have this view.

[defragster]

Stored here: github.com/KurtE/TeensyDocuments

[Fluxanode]

Nevermind found on your git https://github.com/KurtE/TeensyDocum...4.1%20Pins.pdf

[Fluxanode]

thanks Kurt

[gndTeensy]

Thank you I will reference this as I program the board.

[MichaelMeissner]

One thing you might have to be careful about are pins 48-54 that are used for soldering in either 2 PSRAM chips, or 1 PSRAM chaip and 1 flash memory chip. I believe the Teensy initialization functions (called before setup) does a SPI operation to see if there is a PSRAM or flash memory chip attached, and it sets it up if the chips are attached. That SPI operation may confuse any other devices connected to those pins.

[gndTeensy]

One thing you might have to be careful about are pins 48-54 that are used for soldering in either 2 PSRAM chips, or 1 PSRAM chaip and 1 flash memory chip. I believe the Teensy initialization functions (called before setup) does a SPI operation to see if there is a PSRAM or flash memory chip attached, and it sets it up if the chips are attached. That SPI operation may confuse any other devices connected to those pins.

I greatly appreciate your response as this was one of my concerns about the additional pins. I wasn't sure if they are programmed to look for a specific module on startup.

[gndTeensy]

After looking at the pins a bit more, I understand they are only 3.3V tolerant. Sometimes I measure 3.4V when I initialize pullups, but that could just be the volt meter's inaccuracy. Will it be a okay if I have a small pump that sends a signal to the Teensy with a max signal voltage of 3.5V 100mA? I am supplying this small pump with 5V, and the specs state the signals VoutMAX = Vs - 1.5. So mathematically 3.5V is a possible voltage going to the Teensy board's pin. I just wonder if 3.5V will be okay on the pins in the long run.

IF not, I was planning on using a voltage divider with R1=500ohms and R2=10kOhms to bring 3.5V down to 3.3V.

[PaulStoffregen]

Using the resistors would be safest.

[gndTeensy]

One thing you might have to be careful about are pins 48-54 that are used for soldering in either 2 PSRAM chips, or 1 PSRAM chaip and 1 flash memory chip. I believe the Teensy initialization functions (called before setup) does a SPI operation to see if there is a PSRAM or flash memory chip attached, and it sets it up if the chips are attached. That SPI operation may confuse any other devices connected to those pins.

Is there a guide on how to reconfigure this software initialization call because currently I am not using PSRAM chips and flash memory chips.

[defragster]

One thing you might have to be careful about are pins 48-54 that are used for soldering in either 2 PSRAM chips, or 1 PSRAM chaip and 1 flash memory chip. I believe the Teensy initialization functions (called before setup) does a SPI operation to see if there is a PSRAM or flash memory chip attached, and it sets it up if the chips are attached. That SPI operation may confuse any other devices connected to those pins.

That seems localized to: FLASHMEM void configure_external_ram() in startup.c.

Wondering if making that a 'weak' function would allow a sketch to stop the pin chatter searching for PSRAM. Seems it does this one line when no PSRAM found - not sure if that would need to be replicated?
> memset(&extmem_smalloc_pool, 0, sizeof(extmem_smalloc_pool));