I-38
EPSON
S1C6S3N2 TECHNICAL HARDWARE
CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (Input Ports)
However, if the interrupt factor flag is read out immedi-
ately after key scanning, the delay will cause the flag to
be set after read-out, so that it will not be reset.
(3) Input interrupt programing related precautions
Port K input
Factor flag set Not set
➁
Factor flag set
Differential register
Mask register
Active status
Active status
Rising edge interrupt
➀
Falling edge interrupt
When the content of the mask register is rewritten, while the port K
input is in the active status. The input interrupt factor flags are set
at
➀
and
➁
,
➀
being the interrupt due to the falling edge and
➁
the
interrupt due to the rising edge.
Fig. 4.4.4
Input interrupt timing
When using an input interrupt, if you rewrite the content
of the mask register, when the value of the input terminal
which becomes the interrupt input is in the active status,
the factor flag for input interrupt may be set. Therefore,
when using the input interrupt, the active status of the
input terminal implies
input terminal = Low status, when the falling edge
interrupt is effected and
input terminal = High status, when the rising edge
interrupt is effected.
When an interrupt is triggered at the falling edge of an
input terminal, a factor flag is set with the timing of
➀
shown in Figure 4.4.4. However, when clearing the con-
tent of the mask register with the input terminal kept in
the Low status and then setting it, the factor flag of the
input interrupt is again set at the timing that has been
set.
Consequently, when the input terminal is in the active
status (Low status), do not rewrite the mask register
(clearing, then setting the mask register), so that a factor
flag will only set at the falling edge in this case. When
clearing, then setting the mask register, set the mask
register, when the input terminal is not in the active
status (High status).
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