---------------------------------------------------------------HMCS404C
•
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
n
to
PC
o
) with 14-bit immediate data.
•
Current
Page
Addressing
Mode
MCV
has 8 pages
of
ROM(256 words
in
each page).The pro-
gram branches to the address
in
the same page using
BR
instruc-
tion. This instruction replace the low-order eight bits
of
pro-
(JMPL)
(BRL)
(CALL)
Instruction
1st
Word
gram counter (pC
7
to
PC
o
)
with 8-bit immediate data.
•
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
ei~lt
bits (pCl3
to
PC
e
).
The branch destination by
BR
instruction
on the broundary between pages
is
given
in Fig. 24.
•
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"
PC
12
PC
II
PC
••
PC. PC,
(b) Current
Page
Addressing
(e)
Zero
Page
Addressing
Instruction
OP
Code
Program Counter
(d)
Table Data Addressing
Fig. 22
ROM Addressing Mode
251
Instruction
Instruction
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