Wire seems to be working fine, but Wire1 doesn't even show up on a scanner.

[JoshuaACNewman]

I've got a PCB here with a RasPi Pico2350 running my firmware. Things seem to be ok, optmiziation notwithstanding.

I am using 8x MCP4725 DACs. The first four are on i2c bus0 with both the A and B versions, so with ground/Vcc pins set they cover 0x060, 061, 062, and 063. The second four are on Wire1, i2c bus 1, with the same set of DACs and pin settings.

Continuity is correct between pins GP10 (SDA) and GP11 (SCL).

I'm ignoring my main code because I fell back to an i2c scanner firmware (at the bottom) and the results were:

I2C Scan
Wire0 SDA: 0 SCL: 1
I2C device found at address 0x61
I2C device found at address 0x62
Scan Complete

(Note that the missing addresses are due to a hardware configuration error. Given that error, this is correct, and bus1 should list the same addresses.

Wire1 SDA: 2 SCL: 3
No I2C devices found

Wire0 SDA: 4 SCL: 5
No I2C devices found

Wire1 SDA: 6 SCL: 7
No I2C devices found

Wire0 SDA: 8 SCL: 9
No I2C devices found

Wire1 SDA: 10 SCL: 11
No I2C devices found

That's where the other ones should show up, pins GP10 and GP11

Wire0 SDA: 12 SCL: 13
No I2C devices found

Wire1 SDA: 14 SCL: 15
No I2C devices found

Wire0 SDA: 16 SCL: 17
No I2C devices found

Wire1 SDA: 18 SCL: 19
No I2C devices found

Wire0 SDA: 20 SCL: 21
No I2C devices found

Wire1 SDA: 26 SCL: 27
No I2C devices found

All Scans Successful!

The code, which I just downloaded and haven't modified:

// I2C_Scanner - scans all Wire and Wire interfaces on Pico for devices
// Specific pins must be set for both interfaces

#include <Wire.h>

byte error, address;
unsigned int nDevices;
unsigned int wireN = 0;

// Pi Pico SDA/SCL Pins
const unsigned int SDA_00 = 0;
const unsigned int SCL_00 = 1;
const unsigned int SDA_10 = 2;
const unsigned int SCL_10 = 3;
const unsigned int SDA_01 = 4;
const unsigned int SCL_01 = 5;
const unsigned int SDA_11 = 6;
const unsigned int SCL_11 = 7;
const unsigned int SDA_02 = 8;
const unsigned int SCL_02 = 9;
const unsigned int SDA_12 = 10;
const unsigned int SCL_12 = 11;
const unsigned int SDA_03 = 12;
const unsigned int SCL_03 = 13;
const unsigned int SDA_13 = 14;
const unsigned int SCL_13 = 15;
const unsigned int SDA_04 = 16;
const unsigned int SCL_04 = 17;
const unsigned int SDA_14 = 18;
const unsigned int SCL_14 = 19;
const unsigned int SDA_05 = 20;
const unsigned int SCL_05 = 21;
const unsigned int SDA_15 = 26;
const unsigned int SCL_15 = 27;


// scan the Wire interface for devices
void scan_Wire(unsigned int SDA, unsigned int SCL, TwoWire &Wire);

void setup() {
    Serial.begin(115200);
    while (!Serial) {delay(100);}
    Serial.println("\nI2C Scan");

    scan_Wire(SDA_00, SCL_00, Wire);
    scan_Wire(SDA_10, SCL_10, Wire1);
    scan_Wire(SDA_01, SCL_01, Wire);
    scan_Wire(SDA_11, SCL_11, Wire1);
    scan_Wire(SDA_02, SCL_02, Wire);
    scan_Wire(SDA_12, SCL_12, Wire1);
    scan_Wire(SDA_03, SCL_03, Wire);
    scan_Wire(SDA_13, SCL_13, Wire1);
    scan_Wire(SDA_04, SCL_04, Wire);
    scan_Wire(SDA_14, SCL_14, Wire1);
    scan_Wire(SDA_05, SCL_05, Wire);
    scan_Wire(SDA_15, SCL_15, Wire1);

    Serial.println("All Scans Successful!\n");
}


void loop() {

    ;
}

// scan the Wire interfaces for devices
void scan_Wire(unsigned int SDA, unsigned int SCL, TwoWire &Wire)
{
    Wire.setSDA(SDA);
    Wire.setSCL(SCL);
    Wire.begin();

    Serial.print("Wire");
    Serial.print(wireN % 2);
    Serial.print(" SDA: ");
    Serial.print(SDA);
    Serial.print(" SCL: ");
    Serial.println(SCL);

    nDevices = 0;
    for(address = 1; address < 127; address++ ) 
    {
        // The i2c_scanner uses the return value of
        // the Write.endTransmisstion to see if
        // a device did acknowledge to the address.
        Wire.beginTransmission(address);
        error = Wire.endTransmission();

        if (error == 0)
        {
            Serial.print("I2C device found at address 0x");
            if (address<16) 
              Serial.print("0");
            Serial.println(address,HEX);
            nDevices++;
        }
        else if (error==4) 
        {
            Serial.print("Unknown error at address 0x");
            if (address<16)
            { 
                Serial.print("0");
            }
            Serial.println(address,HEX);
        }    
    }
    if (nDevices == 0)
    {    
        Serial.println("No I2C devices found\n");
    }
    else
    {
      Serial.println("Scan Complete\n");
    }
    Wire.end();
    wireN++;
    // End of Wire Scanning Section

}

[earlephilhower]

Do you have test points on both I2C busses? Can you capture them and see? That'd probably be the only way to really see what's going on with a custom PCB.

I just ran the Wire/TalkingToMyself example and added a jumper from GP0->GP2, GP1->GP3 on a Pico 2 board and comms seems to be fine. Both sides can send and receive data and assign pins (before begin of course).

[JoshuaACNewman]

Yeah, I even checked from the top of the pin to make sure it wasn't a broken connection inside the header or something. There is continuity from pin GP10 to SDA and GP11 to SCL.

I thought it might have been where/how I was Wire1.beginning, but now that the scanner code is also failing I don't think it's that.

What does the ampersand mean in &Wire/&Wire1? I don't understand that syntax, but that seems to be where it's failing in my own DAC code so I'd like to at least know what I'm doing so I can figure out what I'm doing wrong.

[earlephilhower]

That code us doing pass by reference, which is like passing the address of the object but you don't need to derefernce it to use it (i.e. W.xxx vs W->xxx). It's used in several spots in the core here and should be fine w/Wire and Wire1 instances.

Not sure where you got that scanner code, but since you only have 1 I2C and 1 set of pins hardwired (Wire1 and GP10/11) why not just write a simple sketch that straight-line does the probe. You can capture the pins on a logic analyzer and have a very simple test case. No need to scan every pin (you know there's nothing else) or Wire (you know it works fine).

[earlephilhower]

And just on the HW side, it's not unknown for PCB houses to stuff the wrong resistor. You may want to check your pull-up resistor value just for sanity's sake. If they put in a 10 ohm instead of a 10k then the Pico would never be able to drive it...

[JoshuaACNewman]

Update: It would appear that there's an electronic problem — pullups are 5V, which is making 3.3v LOW insufficiently low. Thank you for helping me reason this out!

(Why does it work on the other bus? Unlcear! But it's further away on the PCB and may have juuuust enough resistance on the line that the pullups are reduced?)