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TOSHIBA
LO
LO
LO
LO
TMP90C840
As shown in the code format, a I-byte opcode instruction has an opcode
in the first byte and operand codes in the subsequent bytes.
If there
are two I-byte operand codes, the lower operand is placed before the
upper operand.
If both a source and a destination are included as
operand codes, the destination is placed first.
A 2-byte opcode instruction begins with the first opcode, followed by
an operand code specified by the first opcode, then the second opcode
and its operand code.
For example,
B,C
I
1st
°E
Code
I
2nd
°E
Code
I
B, (n)
11 st
°E
Codel
n
12nd
°E
Code!
B,(IX+d) lIst
°E
Codel
d
12nd
°E
Code
I
B, (mn)
11 st
°E
Code!
n
m
12nd
°E
Codel
ADO B,n
lIst
°E
Code 12nd
°E
Code!
n
ADD (VW) ,n
11 st 0p Codel
w
v
12nd 0p Codel
n
In a 2-byte opcode instruction, the pos1t1on of the second opcode is
determined by the first opcode.
Basically,
the first opcode
in a
2-byte
opcode
instruction
provides
data
to
select
the
mode
of
addressing the operand in the range of EOH to FER.
The first operand
code
that
follows
the
first
opcode
serves
to
specify
the memory
addressing mode.
The second operand code that follows
the second
opcode specifies the immediate addressing mode.
Their roles can be
summarized as follows:
I
I
I
1st opcode 11 st operand codel 2nd opcode
2nd operand codel
I
I
I
I
<Specify
>1<
Specify
>1 <
. f
Spec1 y
>1< Specify im-
>1
I
addressing
I
memory
I
instruction
I
mediate ad-
I
mode
addressing
dress ing
MPU90-23
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