LDR Instruction

Note: This was originally posted on 5th November 2008 at http://forums.arm.com

Hi all,
        I am new to the thumb-2 instruction set. In one of my sample code
I noticed a instruction
         LDR r0, =0x12345678;
        This instruction actually load the r0 with value (0x12345678).
But I didn't find such an instruction anywhere in the thumb-2 instruction set.
I am wondering anyone is aware of such instruction and from where i can find
more details about the thumb-2 instruction set.