17
MITSUBISHI MICROCOMPUTERS
4551 Group
SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER for
INFRARED REMOTE CONTROL TRANSMITTER
(1) External 0 interrupt request flag (EXF0)
External 0 interrupt request flag (EXF0) is set to “1” when a
valid waveform is input to D
5
/INT pin.
The valid waveforms causing the interrupt must be retained
at their level for 4 cycles or more of the system clock (Refer
to Figure 16).
The state of EXF0 flag can be examined with the skip
instruction (SNZ0). Use the interrupt control register V1 to
select the interrupt or the skip instruction. The EXF0 flag is
cleared to “0” when an interrupt occurs or when the next
instruction is skipped with the skip instruction.
The D
5
/INT pin need not be selected the external interrupt
input INT function or the normal output port D
5
function.
However, the EXF0 flag is set to “1” when a valid waveform
output from port D
5
is input to INT pin even if it is used as an
output port D
5
.
G
External 0 interrupt activated condition
External 0 interrupt activated condition is satisfied when a
valid waveform is input to D
5
/INT pin.
The valid waveform can be selected from rising waveform or
falling waveform. An example of how to use the external 0
interrupt is as follows.
Select the valid waveform with the bit 2 of register I1.
Clear the EXF0 flag to “0” with the SNZ0 instruction.
Set the NOP instruction for the case when a skip is performed
with the SNZ0 instruction.
Set both the external 0 interrupt enable bit (V1
0
) and the
INTE flag to “1.”
The external 0 interrupt is now enabled. Now when a valid
waveform is input to the D
5
/INT pin, the EXF0 flag is set to
“1” and the external 0 interrupt occurs.
(2) External interrupt control register
G
Interrupt control register I1
Register I1 controls the valid waveform for the external 0
interrupt. Set the contents of this register through register A
with the TI1A instruction. The TAI1 instruction can be used
to transfer the contents of register I1 to register A.
Table 8 External interrupt control register
Notes 1: “R” represents read enabled, and “W” represents write enabled.
2: Depending on the input state of D
5
/INT pin, the external interrupt request flag EXF0 may be set to “1” when the contents of
I1
2
is changed. Accordingly, set a value to bit 2 of register I1 and execute the SNZ0 instruction to clear the EXF0 flag after
executing at least one instruction.
I1
3
I1
2
I1
1
I1
0
Not used
Interrupt valid waveform for INT pin
selection bit (Note 2)
Not used
Not used
0
1
0
1
0
1
0
1
This bit has no function, but read/write is enabled.
Falling waveform (“L” level of INT pin is recognized with the SNZI0
instruction)
Rising waveform (“H” level of INT pin is recognized with the SNZI0
instruction)
This bit has no function, but read/write is enabled.
This bit has no function, but read/write is enabled.
Interrupt control register I1
R/W
at reset : 0000
2
at power down : state retained