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CHAPTER 14 DTP/EXTERNAL INTERRUPT CIRCUIT
14.5.2 DTP Function
The DTP/external interrupt circuit has a DTP (Data Transfer Peripheral) function that
detects the data transfer request signal input to an external interrupt input pin (INT7 to
INT0) from external peripheral devices and activates the extended intelligent I/O
service.
s Operation of the DTP Function
The DTP function is a function for detecting the data transfer request signal input to an external
interrupt input pin (INT7 to INT0) from external peripheral devices to automatically transfer data
between memory and the peripheral devices.
The extended intelligent I/O service is activated by the external interrupt function. The operation
of the DTP function is the same as that of the external interrupt function until an interrupt
request is accepted by the CPU. If the EI2OS operation is enabled (ICR: ISE="1"), EI2OS is
activated when an interrupt request is accepted to start data transfer. When the data transfer is
completed, the descriptor is updated and the external interrupt request flag bit (EIRR: ER7 to
ER0) is cleared to "0" to operate as the external interrupt function again. When the transfer by
EI2OS is completed, branching to the interrupt processing routine pointed to by the vector
address of the external interrupt occurs.
Peripheral devices that are externally connected
should remove the cause input of the data transfer request signal (DTP cause) within three
machine cycles after the first transfer started.
Figure 14.5-4 Example of Interfacing with External Peripheral Devices (Timing)
Input to the INT0 pin
(DTP external interrupt cause)
Internal operation of the
CPU (microprogram)
Address bus pin
Data bus pin
Read signal
Write signal
Descriptor selection
and reading
Read address
Write address
Read data
Write address
H-level request (ELVR: LB0, LA0 = "01B")
Descriptor
updating
*1
*1: Remove within three machine cycles of start of transfer