
9.4 Operations
MB90580 Series
Chapter 9: DTP/External Interrupt
113
9.4.2 DTP operation
To activate the intelligent I/O service, the user program initially sets the address of a register, assigned
between 000000
H
and 0000FF
H
, in the I/O address pointer of the intelligent I/O service descriptor. Then,
the user program sets the start address of the memory buffer in the buffer address pointer.
The DTP operation sequence is almost the same as for external interrupts. The operation is identical until
the CPU activates the hardware interrupt processing microprogram. Then, for the DTP, control is
transferred to the intelligent I/O service processing microprogram, since the ISE bit read by the CPU within
the hardware interrupt processing microprogram indicates the DTP. Once the intelligent I/O service is
activated, a read or write signal is sent to the addresses external peripheral, and data is transferred
between the peripheral and the chip. The external peripheral must cancel the interrupt request to this chip
within three machine cycles after the transfer is made. When the transfer is completed, the descriptor is
updated, and the interrupt controller generates a signal that clears the transfer cause. Upon receiving the
signal to clear the transfer cause, this resource clears the flip-flop holding the cause and prepares for the
next request from the pin. For details of the intelligent I/O service processing, refer to the MB90700
Programming Manual.
Figure 9.4.2a Timing to cancel the external interrupt at the end of DTP operation
Figure 9.4.2b Sample interface to the external peripheral
Interrupt cause
Internal operation
Address bus pin
Data bus pin
Read signal
Write signal
Selecting and
reading
descriptor
Edge request or H level request
* When data is transferred from the I/O register to memory
in the intelligent I/O service
Read address
Write address
Read data
Write data
Cancel within three machine cycles.
Data, address
bus
DTP
CORE
MEMORY
MB90580
INT
IRQ
E
R
Internal bus
Cancel within three machine
cycles after transfer.