##### 9.24.2.3 Register Names

General-purpose registers are represented by predefined symbols of the form ``rN`' (for global registers), where N represents a number between `0` and `15`. The leading letters may be in either upper or lower case; for example, ``r13`' and ``R7`' are both valid register names.

Register names ``PC`', ``SP`' and ``SR`' cannot be used as register names and will be treated as variables. Use ``r0`', ``r1`', and ``r2`' instead.