
I-32
EPSON
S1C62N33 TECHNICAL HARDWARE
CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (Input Ports)
From the status of these flags, the software can decide
whether an input interrupt has occurred.
These flags are reset when the software reads them. Read-
out can be done only in the DI status (interrupt flag = "0").
At initial reset, these flags are set to "0".
(1) When input ports are changed from high to low by pull-
down resistance, the fall of the waveform is delayed on
account of the time constant of the pull-down resistance
and input gate capacitance. Hence, when fetching input
ports, set an appropriate wait time.
Particular care needs to be taken of the key scan during
key matrix configuration. Aim for a wait time of about 1
ms.
(2) When "noise rejector circuit enable" is selected with the
mask option, a maximum delay of 1 ms occurs from time
the interrupt conditions are established until the inter-
rupt factor flag (IK) is set to "1" (until the interrupt is
actually generated).
Hence, pay attention to the timing when reading out
(resetting) the interrupt factor flag.
For example, when performing a key scan with the key
matrix, the key scan changes the input status to set the
interrupt factor flag, so it has to be read out to reset it.
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
Programming notes
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
and , being the interrupt due to the falling edge and the
interrupt due to the rising edge.
Fig. 4.4.4
Input interrupt timing
Port K input
Factor flag set Not set
Factor flag set
Differential register
Mask register
Active status
Rising edge interrupt
Falling edge interrupt