The value of R0 is always 0. Bytes and half words are loaded into registers with either zeros or the sign bit replicated to fill the 32 bits of the registers. Register deferred and absolute addressing with 16-bit field are accomplished using R0. All ALU instructions are register-register instructions. If the condition is true, these instructions place a 1 in the destination register, otherwise they place a 0.
All branches are conditional.
The branch condition is specified by the instruction, which may test the register source for zero or nonzero.