2.6.4 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).
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: Eight, 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.
Figure 2-9 Instruction Formats
op
NOP, RTS, etc.
op
rn
rm
op
rn
rm
EA (disp)
Operation field only
ADD.B Rn, Rm, etc.
Operation field and register fields
MOV.B @(d:16, Rn), Rm
Operation field, register fields, and effective address extension
BRA d:8
Operation field, effective address extension, and condition field
op
cc
EA (disp)
38
www.DataSheet4U.com