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2.7.3
Basic Instruction Formats
The H8SX CPU 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).
Figure 2.14 shows examples of instruction formats.
(1) Operation field only
(2) Operation field and register fields
(3) Operation field, register fields, and effective address extension
(4) Operation field, effective address extension, and condition field
op
• 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 four 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.
• Condition Field
Specifies the branching condition of Bcc instructions.
op
op
rn
op
EA (disp)
cc
Figure 2.14 Instruction Formats
NOP, RTS, etc.
rm
ADD.B Rn, Rm, etc.
rn
rm
MOV.B @(d:16, Rn), Rm, etc.
EA (disp)
BRA d:16, etc
Rev.2.00 Jun. 28, 2007 Page 49 of 666
Section 2 CPU
REJ09B0311-0200
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