How to expect number or letter

[AbdulkerimFettahoglu]

Users can write number or letter to text. First two characters can be 'A' or '1'. I've checked the examples but can't found. My pattern should be something like following:

<div>
   <label for="myFormat">My Format Label</label>
   <input id="myFormat" placeholder="XX XX XXX" pattern="([A-Z]|[0-9]){2} \d\d \d\d\d" 
   class="masked" data-charset="__ XX XXX"
   type="text" name="myFormatName"/>
</div>