Arduino UNO + 2x Seeed Studio CAN BUS Shield V2, MCP_CAN_lib help

Projects General Guidance
1

Hello im working on reverse engineering a 2019 Jeep Cherokee cluster, ive been able to connect to CAN-C with one shield but I cannot get the second shield to connect to CAN-IHS.
I have both shields stacked on the UNO and they both have pin 9 default CS pin and pin 2 default INT pin
I am using MCP_CAN_lib by coryjfowler

#include <mcp_can.h>
#include <SPI.h>

// Define chip select pins for each MCP2515 CAN controller
MCP_CAN CAN0(9);   // CAN-C on CS pin 9
MCP_CAN CAN1(10);  // CAN-IHS on CS pin 10

void setup() {
  Serial.begin(115200);
  SPI.begin();

  // Initialize CAN-C (500 kbps, standard CAN)
  if (CAN0.begin(MCP_ANY, CAN_500KBPS, MCP_16MHZ) == CAN_OK) {
    Serial.println("CAN-C Initialized Successfully!");
  } else {
    Serial.println("Error Initializing CAN-C...");
  }

  // Initialize CAN-IHS (125 kbps, extended CAN)
  if (CAN1.begin(MCP_ANY, CAN_125KBPS, MCP_16MHZ) == CAN_OK) {
    Serial.println("CAN-IHS Initialized Successfully!");
  } else {
    Serial.println("Error Initializing CAN-IHS...");
  }

  // Set both controllers to normal mode
  CAN0.setMode(MCP_NORMAL);
  CAN1.setMode(MCP_NORMAL);
}

// Send message to CAN-C using standard 11-bit ID
void sendCAN_C(int identifier, int dlc, byte data[]) {
  byte result = CAN0.sendMsgBuf(identifier, MCP_STD, dlc, data);
  Serial.println(result == CAN_OK ? "Sent on CAN-C!" : "Failed to send on CAN-C...");
}

// Send message to CAN-IHS using extended 29-bit ID
void sendCAN_IHS(int identifier, int dlc, byte data[]) {
  byte result = CAN1.sendMsgBuf(identifier, MCP_EXT, dlc, data);
  Serial.println(result == CAN_OK ? "Sent on CAN-IHS!" : "Failed to send on CAN-IHS...");
}

void loop() {
  if (Serial.available()) {
    char input[64] = {0};
    Serial.readBytesUntil('\n', input, sizeof(input) - 1);
    Serial.print("Received: ");
    Serial.println(input);

    // Parse input: ID,DLC,DATA0,DATA1,...
    char *token = strtok(input, ",");
    if (!token) return;
    int identifier = atoi(token);

    token = strtok(NULL, ",");
    if (!token) return;
    int dlc = atoi(token);
    if (dlc < 0 || dlc > 8) return;

    byte data[8] = {0};
    for (int i = 0; i < dlc; i++) {
      token = strtok(NULL, ",");
      if (token) data[i] = (byte)atoi(token);
    }

    // Debug: Print data bytes
    Serial.print("Data (HEX): ");
    for (int i = 0; i < dlc; i++) {
      Serial.print("0x");
      if (data[i] < 0x10) Serial.print("0");
      Serial.print(data[i], HEX);
      Serial.print(" ");
    }
    Serial.println();

    sendCAN_C(identifier, dlc, data);
    sendCAN_IHS(identifier, dlc, data);
  }
}

still learning as I go, sorry if its a simple fix

2

Your text and sketch seem to be inconsistent. If both shields are indeed using pin 9 for CS, it definitely won't work.

And this seems unlikely to work as well, even if both shields have open collector/drain outputs and not totem pole.

3

Sorry I wasn’t clear, I want the second bus to use pin 10 for CAN-IHS, the default is 9 and I can’t change it, same for INT. I understand they can’t use the same pins.

4

If you look at the documentation for the v2 CAN bus shield, it says the INT pin can be D2 or D3 by setting a jumper on the back of the board. It also appears there is CS_A (D9) and CS_B (D10) that is selectable via jumper as well.