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CHAPTER 16 DTP/EXTERNAL INTERRUPTS
16.5 Precautions on Use of DTP/External Interrupt Unit
This section shows precautions on use of the DTP/external interrupt unit.
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Conditions for external connection of peripheral devices
For support by the DTP unit, external peripheral devices must be able to automatically clear a
request after successful data transfer. If a transfer request fails to be withdrawn within three
machine cycles after the transfer operation starts (interim value), the DTP unit will proceed as if
a new transfer request had been generated.
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Procedures for DTP/external interrupt unit operation
Set the values of registers in the DTP/external interrupt unit as follows:
(1) Set the pin used as an external interrupt input and the general-purpose I/O port used
combinedly to the input port.
(2) Set the bits for the registers (ENIR) to be enabled to "disable".
(3) Set the bits of the request level setting register (ELVR).
(4) Clear the bits in the source register (EIRR).
(5) Set the bits for the registers (ENIR) to be enabled to "enable".
Steps (4) and (5) allow simultaneous writing by word-length specification.
To set the contents of DTP/external interrupt unit registers, first disable the registers to be
enabled. Before enabling the registers to be enabled again, clear the source register in order to
avoid accidental generation of an interrupt source in register setting of interrupt enabled state.
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