--------------------------------------------------------------------------HMCS404CL
•
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 10-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
(10
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 Y -Register
r-----------.",,.------__.
(a)
Register Indirect Addressing
Instruction
, st
Word
Instruction
2nd
Word
(b) Direct Addressing
"0" "0"
000"
000"
00'"
000"
RAM Address
(c) Memory Register Addressing
Fig.21 RAM Addressing Mode
363
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