Epson S1C6S3N2, Technical Manual

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S1C6S3N2 TECHNICAL HARDWARE
EPSON
I-37
CHAPTER 4: PERIPHERAL CIRCUITS AND OPERATION (Input Ports)
These flags indicate the occurrence of input interrupt.
When "1" is read out : Interrupt has occurred
When "0" is read out : Interrupt has not occurred
Writing : Invalid
The interrupt factor flags IK0 and IK1 are associated with
K00–K03 and K10, respectively. 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.
Reading of interrupt factor flags is available at EI, but be
careful in the following cases.
If the interrupt mask register value corresponding to the
interrupt factor flags to be read is set to "1", an interrupt
request will be generated by the interrupt factor flags set
timing, or an interrupt request will not be generated.
Be very careful when interrupt factor flags are in the same
address.
At initial reset, these flags are set to "0".
IK0, IK1:
Interrupt factor flags
(07AH·D2 and D3)
(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.
Programming notes