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CHAPTER 14 DTP/EXTERNAL INTERRUPT CIRCUIT
14.6 Usage Notes on the DTP/External Interrupt Circuit
Notes on the signal to be input to the DTP/external interrupt circuit, release from
standby mode, and interrupts are given below.
s Usage Notes on the DTP/External Interrupt Circuit
r Conditions for external peripherals using the DTP function
To support the DTP function, peripheral devices that are externally connected must be able to
automatically clear data transfer requests after transfer is carried out. If an externally connected
peripheral device continues to output a transfer request longer than three machine cycles after
the CPU started the transfer operation, the DTP/external interrupt circuit interprets the request
as another transfer request and performs the data transfer operation again.
r Input polarities of external interrupts
If the request level setting register (ELVR) is set for edge detection, the pulse width of at
least three machine cycles is required from the point of change of the input level to detect
the input of an edge that is to become an interrupt request.
If the request level setting register (ELVR) is set for level detection, and the level for interrupt
request is input, the cause flip-flop in the DTP/interrupt cause register (EIRR) is set to "1"
and retains the cause, as shown in
Figure 14.6-1 "Clearing the Cause Retention Circuit
When a Level is Specified". Thus, even if the interrupt cause is removed, the request to the
interrupt controller remains active. To cancel the request to the interrupt controller, set the
external interrupt request flag bits (EIRR: ER7 to ER0) to "0" to clear the cause flip-flop to
Specified".
Figure 14.6-1 Clearing the Cause Retention Circuit When a Level is Specified
DTP/external
interrupt cause
To the interrupt
controller
(interrupt request)
DTP/interrupt input
detection circuit
Cause FF
(in the EIRR register)
Enable gate
The cause is stored until the register is cleared.