2.1.5 Register Specification
Address Register Specification: When a general register is used as an address register [@ERn,
@(d:16, ERn), @(d:24, ERn), @ERn+, or @–ERn], the register is specified by a 3-bit register
field (ers or erd). The lower 24 bits of the register are valid.
Data Register Specification: A general register can be used as a 32-bit, 16-bit, or 8-bit data
register, which is specified by a 3-bit register number. When a 32-bit register (ERn) is used as a
longword data register, it is specified by a 3-bit register field (ers, erd, or ern). When a 16-bit
register is used as a word data register, it is specified by a 4-bit register field (rs, rd, or rn). The
lower 3 bits specify the register number. The upper bit is set to 1 to specify an extended register
(En) or cleared to 0 to specify a general register (Rn). When an 8-bit register is used as a byte data
register, it is specified by a 4-bit register field (rs, rd, or rn). The lower 3 bits specify the register
number. The upper bit is set to 1 to specify a low register (RnL) or cleared to 0 to specify a high
register (RnH). This is shown next.
Address Register
32-bit Register
16-bit Register
8-bit Register
Register General
Register General Register
General
Field
Register
Field
Register
Field
Register
000
ER0
0000
R0
0000
R0H
001
ER1
0001
R1
0001
R1H
111
ER7
0111
R7
0111
R7H
1000
E0
1000
E0L
1001
E1
1001
E1L
1111
E7
1111
E7L
39