Hi,
I'm far newer to the forum than to Arduino and I usually find my answers without annoying other people with questions like this 
I nearly gave up in trying to understand this and I can't let that happen. So i reach out to you and hope, someone can explain me why I get this behaviour.
I'm currently working on a small weather station project -> AtTiny85 reporting DHT22 data through 433MHz transmitter to an UNO which itself has a DHT22 Sensor and additional 2x16 LCD to display both readings.
Details to be found here: diy-funk-wetterstation-mit-dht22-attiny85-und-radiohead
I got it working but something is puzzling me and I fail to get the AHA experience.
On the receiver side (UNO)
If I define the DHT_Pin like so: [#define DHT_PIN 9] I won't get any readings. However, if I use [#define DHT_PIN PB1] it works like a charm.
From AtTiny85 I'm used to "strange" pin names. But not on the UNO...
The strange thing about it is: The Pins for the receiver module and the LCD Module are defined with the pin number and they work fine this way.
On this Forum I found a hint regarding the file hardware\arduino\avr\variants\standard\pins_arduino.h but I don't see anything wrong with it. (pin 9 is only mentioned once as declaration for a digital pwm pin on row 35)
Any Ideas why I cant access the DHT Sensor through pin 9?
IDE v1.8.9, target board Arduino/Genuino UNO
// source https://git.cryhost.de/crycode/attiny85-radiohead-dht22-weather-sensor/snippets/19
#define SERVER_ADDRESS 0x01
#define RH_SPEED 2000
#define RH_RX_PIN 5
#define LED_PIN 13
#define DHT_PIN PB1 //pin 9
#define RH_BUF_LEN 9
uint8_t rh_buf[RH_BUF_LEN];
#define RH_ASK_MAX_MESSAGE_LEN RH_BUF_LEN
#include <RHDatagram.h>
#include <RH_ASK.h>
//LCD Stuff
#include <LiquidCrystal.h>
const int rs = 12, en = 11, d4 = 6, d5 = 4, d6 = 3, d7 = 2;
LiquidCrystal lcd(rs, en, d4, d5, d6, d7);
#include "dht22.h"
dht22 dht;
RH_ASK driver(RH_SPEED, RH_RX_PIN);
RHDatagram manager(driver, SERVER_ADDRESS);
float t = 0;
float h = 0;
uint8_t bat_percent = 0;
uint8_t bat_raw = 0;
void setup() {
 lcd.begin(16, 2);
 Serial.begin(9600);
 if (!manager.init()) {
  Serial.println("init failed");
  lcd.print("init failed");
 } else {
  Serial.println("init done");
  lcd.print("init ok...");
  lcd.setCursor(0, 1);
  lcd.print("wait for input");
 }
 dht_init(&dht, DHT_PIN);
 pinMode(LED_PIN, OUTPUT);
}
void loop() {
 if (manager.available()) {
  uint8_t len = sizeof(rh_buf);
  uint8_t from;
  if (manager.recvfrom(rh_buf, &len, &from)) {
   lcd.clear();
   digitalWrite(LED_PIN, HIGH);
   //Serial.print("got message from : 0x");
   //Serial.println(from, HEX);
   switch (rh_buf[0]) {
    case 0x00:
     // start message
     Serial.println("0x00 start");
     break;
    case 0x01:
     // DHT data
     //Serial.println("0x01 DHT data");
     memcpy(&t, &rh_buf[1], 4);
     memcpy(&h, &rh_buf[5], 4);
     Serial.print(t);
     Serial.print("°C - ");
     Serial.print(h);
     Serial.println("%");
     String lcddata = "O: " + String(t, 1) + char(223) + "C, " + String(h, 1) + "%";
     lcd.setCursor(0, 0);
     lcd.print(lcddata);
     readInsideTemp();
     break;
    case 0x02:
     // battery data
     //Serial.println("0x02 battery data");
     bat_percent = rh_buf[1];
     bat_raw = rh_buf[2];
     Serial.print(bat_percent);
     Serial.print("% Batery - ADC: ");
     Serial.println(bat_raw);
     break;
    case 0xee:
     // error
     Serial.println("0xEE error");
     break;
    default:
     // should never happen
     break;
   }
   digitalWrite(LED_PIN, LOW);
  }
 }
}
void readInsideTemp() {
 float tin = 0;
 float hin = 0;
 String lcddata;
 if (dht_read_data(&dht, &tin, &hin) == 1) {
  lcddata = "I: " + String(tin, 1) + char(223) + "C, " + String(hin, 1) + "%";
 } else {
  lcddata = "I: DHT NOK!";
 }
 lcd.setCursor(0, 1);
 lcd.print(lcddata);
}
Solution:
The Problem is related to the used Fast dht22 library by Sergey Denisov aka LittleBuster GitHub - LittleBuster/avr-dht22: DHT22 library C-language
The library is hardcoded to Port B which played a trick on me.
hence DHT_PIN 1 is equal to Port B Pin 1 which refers to arduino pin 9
2 -> PB2 -> arduino pin 10 etc.
Aka, it's made for "plain" AVR use. A "normal Arduino" is AVR based so you can use that library. But the library has no notion at all of all the Arduino stuff like how the pins are defined. Hence it just uses the direct style.
Well I'm working on that matter 
