MITSUBISHI
ELECTRIC
17
MITSUBISHI MICROCOMPUTERS
4250 Group
SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER
(6) Control register related to interrupt
Timer control register V1
Interrupt enable bits of external and timer 1 are assigned
to register V1. Set the contents of this register through
register A with the TV1A instruction. The TAV1 instruction
can be used to transfer the contents of register V1 to register
A.
(7) Interrupt sequence
Interrupts occur only when the respective INTE flag, interrupt
enable bits (V1
0
, V1
1
), and interrupt request flags (EXF0, T1F)
are “1.” The interrupt actually occurs 2 to 3 machine cycles
after the cycle in which all three conditions are satisfied. The
interrupt occurs after 3 machine cycles only when the three
interrupt conditions are satisfied on execution of other than
one-cycle instructions (Refer to Figure 16).
Fig. 16 Interrupt sequence
Table 6 Control register related to interrupt
V1
3
V1
2
V1
1
V1
0
Timer control register V1
G
1
/T
OUT
pin function selection bit
Prescaler/timer 1 operation start bit
Timer 1 interrupt enable bit
External interrupt enable bit
Port G
1
(I/O)
T
OUT
pin (output)/port G
1
(input)
Prescaler stop (initial state) / timer 1 stop (state retained)
Prescaler / timer 1 operation
Interrupt disabled (SNZ1 instruction is valid)
Interrupt enabled (SNZ1 instruction is invalid)
Interrupt disabled (SNZ0 instruction is valid)
Interrupt enabled (SNZ0 instruction is invalid)
0
1
0
1
0
1
0
1
Note: “R” represents read enabled, and “W” represents write enabled.
at reset : 0000
2
R/W
at RAM back-up : 0000
2
T
1
T
2
T
3
T
4
T
1
T
2
T
3
T
4
T
1
T
2
T
3
T
4
T
1
T
2
T
3
T
4
T
1
T
2
T
3
T
4
2
to 3
machine cycles
(Notes 1, 2)
Software starts from
the interrupt address.
Flag cleared
Interrupt enabled state.
G
When an interrupt request flag is set after its interrupt is enabled
f (X
IN
)
EI instruction
execution cycle
Interrupt enable
flag (INTE)
Retaining level for 5 cycles or more
of f(X
IN
) is necessary.
Interrupt disabled state.
EXF0
flag
T1F flag
G
0
/INT pin
External
interrupt
Timer 1
interrupt
Interrupt activated
condition is satisfied.
1 machine cycle
The address is stacked to the last cycle.
This interval of cycles depends on the executed instruction at the time when each interrupt activated condition is satisfied.
Notes 1:
2: