HMCS404CL--------------------------------------------------------------------------
• ROM ADDRESSING MODE AND P INSTRUCTION
The
MCV
has four kinds
of
ROM addressing modes as shown
in Fig. 22.
• Direct Addressing Mode
The
program can branch to any addresses in
the
ROM
memory
space
by
using JMPL, BRL
or
CALL instruction.
These instruction replace 14-bit program
counter
(PC
l3
to
PC
o
) with 14-bit immediate data.
• Current Page Addressing Mode
ROM
memory
space is divided into
256
words in each page
starting from
$0000. The program branches
to
the
address in
the
same page using BR instruction. This instruction replace
the low-order eight bits
of
program
counter
(pC?
to
PCo)
with
8-bit immediate data. The branch destination
by
BR
(JMPL)
(BRL)
(CALL)
Instruction
1
st
Word
instruction
on
the boundary between pages
is
in the
next
page.
Refer
to
Fig. 24.
• Zero Page Addressing Mode
The
program branches
to
the zero page subroutine area,
which
is
located
on
the
address from
$0000
to
$003F,
using
CAL instruction. When
CAL
instruction
is
executed, 6-bit
immediate
data
is placed in low-order six bits
of
program
counter
(PC
s
to
PC
o
) and '.'O's" are placed in high-order eight
bits
(pC 13
to
PC
6
).
• Table Data Addressing
The program branches to the address determined
by
the
contents
of
the 4-bit immediate data,
accumulator
and B regis-
ter, using TBR instruction.
Instruction
2nd
Word
(a)
Direct Addressing
(TBR)
(BR)
Program Counter PC
H
PC
I2
PC"
PC
IO
PC
9
PC
a
(b) Current
Page
Addressing
(c)
Zero
Page
Addressing
Instruction
Program Counter
(d)
Table Data Addressing
Fig.
22 ROM Addressing Mode
364
Instruction
Instruction
B Register
Accumulator
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