Register Specification - Hitachi H8/300H Series Programming Manual

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
Register General
Field Register
000 ER0
001 ER1
111 ER7
16-bit Register
Register General
Field Register
0000 R0
0001 R1
0111 R7
1000 E0
1001 E1
1111 E7
39
8-bit Register
Register General
Field Register
0000 R0H
0001 R1H
0111 R7H
1000 E0L
1001 E1L
1111 E7L