1-19
3820 GROUP USER’S MANUAL
MITSUBISHI MICROCOMPUTERS
3820 Group
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
INTERRUPTS
Interrupts occur by sixteen sources: seven external, eight internal,
and one software.
Interrupt Control
Each interrupt is controlled by an interrupt request bit, an interrupt
enable bit, and the interrupt disable flag except for the software in-
terrupt set by the BRK instruction. An interrupt occurs if the corre-
sponding interrupt request and enable bits are “1” and the inter-
rupt disable flag is “0”.
Interrupt enable bits can be set or cleared by software.
Interrupt request bits can be cleared by software, but cannot be
set by software.
The BRK instruction cannot be disabled with any flag or bit. The I
(interrupt disable) flag disables all interrupts except the BRK in-
struction interrupt.
Interrupt Operation
When an interrupt is received, the contents of the program counter
and processor status register are automatically stored into the
stack. The interrupt disable flag is set to inhibit other interrupts
from interfering.The corresponding interrupt request bit is cleared
and the interrupt jump destination address is read from the vector
table into the program counter.
Notes on Use
When the active edge of an external interrupt (INT
0
–INT
3
, CNTR
0
,
or CNTR
1
) is changed, the corresponding interrupt request bit
may also be set. Therefore, please take following sequence;
(1) Disable the external interrupt which is selected.
(2) Change the active edge selection.
(3) Clear the interrupt request bit which is selected to “0”.
(4) Enable the external interrupt which is selected.
Interrupt Source
Reset (Note 2)
INT
0
INT
1
Serial I/O1
receive
Serial I/O1
transmit
Timer X
Timer Y
Timer 2
Timer 3
CNTR
0
CNTR
1
Timer 1
INT
2
INT
3
Key input
(Key-on wake up)
Serial I/O2
BRK instruction
Low
FFFC
16
FFFA
16
FFF8
16
FFF6
16
FFF4
16
FFF2
16
FFF0
16
FFEE
16
FFEC
16
FFEA
16
FFE8
16
FFE6
16
FFE4
16
FFE2
16
FFE0
16
FFDE
16
FFDC
16
High
FFFD
16
FFFB
16
FFF9
16
FFF7
16
FFF5
16
FFF3
16
FFF1
16
FFEF
16
FFED
16
FFEB
16
FFE9
16
FFE7
16
FFE5
16
FFE3
16
FFE1
16
FFDF
16
FFDD
16
Table 7. Interrupt vector addresses and priority
Priority
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Interrupt Request
Generating Conditions
At reset
At detection of either rising or
falling edge of INT
0
input
At detection of either rising or
falling edge of INT
1
input
At completion of serial I/O1
data reception
At completion of serial I/O1
transmit shift or when transmit
buffer register is empty
At timer X underflow
At timer Y underflow
At timer 2 underflow
At timer 3 underflow
At detection of either rising or
falling edge of CNTR
0
input
At detection of either rising or
falling edge of CNTR
1
input
At timer 1 underflow
At detection of either rising or
falling edge of INT
2
input
At detection of either rising or
falling edge of INT
3
input
At falling of conjunction of input
level for port P2 (at input mode)
At completion of serial I/O2
data transmission or reception
At BRK instruction execution
Remarks
Non-maskable
External interrupt
(active edge selectable)
External interrupt
(active edge selectable)
Valid when serial I/O1 is selected
Valid when serial I/O1 is selected
External interrupt
(active edge selectable)
External interrupt
(active edge selectable)
External interrupt
(active edge selectable)
External interrupt
(active edge selectable)
External interrupt
(valid when an “L” level is applied)
Valid when serial I/O2 is selected
Non-maskable software interrupt
Vector Addresses (Note 1)
Note 1
: Vector addresses contain interrupt jump destination addresses.
2
: Reset function in the same way as an interrupt with the highest priority.