Info Catalog
as: AVR-Chars
as: AVR Syntax
as: AVR-Modifiers
9.5.2.2 Register Names
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The AVR has 32 x 8-bit general purpose working registers 'r0', 'r1', ...
'r31'. Six of the 32 registers can be used as three 16-bit indirect
address register pointers for Data Space addressing. One of the these
address pointers can also be used as an address pointer for look up
tables in Flash program memory. These added function registers are the
16-bit 'X', 'Y' and 'Z' - registers.
X = r26:r27
Y = r28:r29
Z = r30:r31