Modbus Input Register Read Fails

modbus_read_registers(ctx, 0, 10, reg);  # Wrong! Use modbus_read_input_registers

#include <modbus/modbus.h>

int read_input_registers(modbus_t *ctx) {
  uint16_t input_reg[16];
  
  // Read input registers (function code 0x04)
  int rc = modbus_read_input_registers(ctx, 0, 10, input_reg);
  
  if (rc == -1) {
    printf('Read input registers failed: %s (errno=%d)\n',
           modbus_strerror(errno), errno);
    
    // Check specific errors
    if (errno == EMBBADCRC) {
      printf('CRC error — check wiring and baud rate\n');
    } else if (errno == ETIMEDOUT) {
      printf('Timeout — slave not responding\n');
    }
    return -1;
  }
  
  printf('Read %d input registers:\n', rc);
  for (int i = 0; i < rc; i++) {
    printf('  Input[%d] = 0x%04X (%d)\n', i, input_reg[i], input_reg[i]);
  }
  
  return 0;
}

// Expected: Input[0] = 0x0FA0 (4000) — analog input value