##### 9.29.2.3 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.