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2.5.2
Basic Instruction Formats
The H8/300H instructions consist of 2-byte (1-word) units. An instruction consists of an operation
field (OP field), a register field (r field), an effective address extension (EA field), and a condition
field (cc field).
Operation Field: Indicates the function of the instruction, the addressing mode, and the operation
to be carried out on the operand. The operation field always includes the first 4 bits of the
instruction. Some instructions have two operation fields.
Register Field: Specifies a general register. Address registers are specified by 3 bits, data registers
by 3 bits or 4 bits. Some instructions have two register fields. Some have no register field.
Effective Address Extension: 8, 16, or 32 bits specifying immediate data, an absolute address, or
a displacement. A 24-bit address or displacement is treated as 32-bit data in which the first 8 bits
are 0 (H'00).
Condition Field: Specifies the branching condition of Bcc instructions.
Figure 2.9 shows examples of instruction formats.
Operation field only
Operation field and register fields
Operation field, register fields, and effective address extension
Operation field, effective address extension, and condition field
op
32
op
op
op
EA (disp)
cc
Figure 2.9 Instruction Formats
rn
rm
rn
rm
EA (disp)
NOP, RTS, etc.
ADD.B Rn, Rm, etc.
MOV.B @(d:16, Rn), Rm
BRA d:8
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