-----------------------------------------------------------------------------HMCS404AC
• RAM ADDRESSING MODE
As
shown
in Fig. 21,
the
MeU
provides
three
RAM address-
ing
modes;
Register
Indirect
Addressing, Direct Addressing
and
Memory
Register Addressing.
• Register
Indirect
Addressing
The
combined
IO-bit
contents
of
W Register, X Register
and
Y Register is used as
the
RAM address in this
mode.
RAM
Address
• Direct Addressing
The
direct
addressing
instruction
consists
of
two
words
and
the
second
word
(IO
bits) following Op-code
(the
first
word)
is
used
as
the
RAM address.
• Memory Register Addressing
The
Memory Register Addressing
can
access
16
digits
(Memory Register:
MR)
from
$020
to
$02F
by
using
the
LAMR
and
XMRA
instruction.
.
W-Register X-Register
V-Register
,----------,
(a)
Register Indirect Addressing
Instruction
1 st
Word
Instruction 2nd Word
(b) Direct Addressing
"0"
"0"
"0"
"0"
"1" "0"
RAM
Address
(c)
Memory Register Addressing
Fig.21 RAM Addressing Mode
325
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