HMCS404C----------------------------------------------------------------
•
RAM
ADDRESSING MODE
As shown in Fig. 21,
the
MeV
provides three RAM address-
ing modes; Register Indirect Addressing, Direct Addressing
and
Memory Register Addressing.
• Register Indirect Addressing
The combined lO-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--------..\r"---=----
.....
(a)
Register Indirect Addressing
Instruction
1 st
Word
Instruction
2nd
Word
(b) Direct Addressing
Instruction
"0"
"0" "0" "0"
"1" "0"
RAM Address
(e)
Memory Register Addressing
Fig.
21
RAM Addressing Mode
250
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