61
3886 Group
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
MITSUBISHI MICROCOMPUTERS
PROCESSOR MODE
Single-chip mode, memory expansion mode, and microprocessor
mode in the M38867M8A/E8A can be selected by changing the
contents of the processor mode bits (CM
0
and CM
1
: b1 and b0 of
address 003B
16
). In memory expansion mode and microprocessor
mode, memory can be expanded externally through ports P0 to
P3. In these modes, ports P0 to P3 lose their I/O port functions
and become bus pins.
Fig. 62 Memory maps in various processor modes
Fig. 63 Structure of CPU mode register
(1) Single-chip mode
Select this mode by resetting the microcomputer with CNV
SS
con-
nected to V
SS
.
(2) Memory expansion mode
Select this mode by setting the processor mode bits (b1, b0) to
“01” in software with CNV
SS
connected to V
SS
. This mode enables
external memory expansion while maintaining the validity of the in-
ternal ROM.
However, do not set this mode in the M38869M8A/MCA/MFA and
the flash memory version.
(3) Microprocessor mode
Select this mode by resetting the microcomputer with CNV
SS
con-
nected to V
CC
, or by setting the processor mode bits to “10” in
software with CNV
SS
connected to V
SS
. In microprocessor mode,
the internal ROM is no longer valid and external memory must be
used.
Do not set this mode in the M38869M8A/MCA/MFA and the flash
memory version.
Port Name
Port P0
Port P1
Port P2
Port P3
Function
Outputs low-order 8 bits of address.
Outputs high-order 8 bits of address.
Operates as I/O pins for data D
7
to D
0
(including instruction code).
P3
0
and P3
1
function only as output pins
(except that the port latch cannot be read).
P3
2
is the ONW input pin.
P3
3
is the RESET
OUT
output pin. (
Note
)
P3
4
is the
φ
output pin.
P3
5
is the SYNC output pin.
P3
6
is the WR output pin, and P3
7
is the RD out-
put pin.
Table 15 Port functions in memory expansion mode and
microprocessor mode
Note :
If CNV
SS
is connected to V
SS
, the microcomputer goes to single-
chip mode after a reset, so that this pin cannot be used as the
RESET
OUT
output pin.
X
X
X
1
6
X
X
1
0
0
0
0
1
6
0
4
0
1
6
0
8
1
6
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0
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6
Y
Y
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6
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