Teensy4.1 special features + additional pins

G

gndTeensy

Member
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!
 
Yes you can use those other pins for GPIO stuff.

From my Excel document on T4.x I have the page:
Screenshot.png
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.
 
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.
 
MichaelMeissner said:
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.
Click to expand...

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.
 
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.
 
MichaelMeissner said:
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.
Click to expand...

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

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));
 
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