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3.3 Interrupts
208
Chapter 3:Operation
3.3.3 Extended Intelligent I/O Service (EI2OS)
(1) Overview
The EI2OS is one type of hardware interrupt operation that transfers data automatically between I/O and
memory. This function makes it possible to use DMA transfer to exchange data with I/O. This
exchange has been done by the conventional interrupt processing program. Compared with methods
used in conventional interrupt processing, the EI2OS offers the following benefits.
Because there is no need to describe a transfer program, the program size can be reduced.
Because the internal registers are not used during the transfer, there is no need to save data into
the registers, resulting in a faster transfer speed.
Because I/O can stop the transfer when necessary, unneeded data is not transferred.
It is possible to select whether to increment/decrement or not to update the buffer address.
It is possible to select whether to increment/decrement or not to update the I/O register address
(when there is a buffer address update).
When the EI2OS is terminated, program control automatically branches to the interrupt processing
routine after the termination condition is set, making it possible for the user to determine the
termination condition type.
An overview of the EI2OS is shown in Fig. 3.3.5.
Fig. 3.3.5 Overview of Extended Intelligent I/O Service
[CAUTION]
The area accessible with the I/O address pointer (IOA) is 000000H to 00FFFFH.
The area accessible with the buffer address pointer (BAP) is 000000H to FFFFFFH.
The maximum number of transfer that can be designated by the data counter registers
(DCTH/DCTL) is 65,536.
Memory space
I/O register
Buffer
I/O register
Interrupt request
Interrupt control register
Interrupt controller
ISD
by IOA
by BAP
(4)
(1)
(3)
Peripheral
by ICS
(2)
(1) I/O requests transfer.
(2) The interrupt controller selects the
descriptor.
(3) The transfer source and destination
are read from the descriptor.
(4) The transfer between I/O and memory
is performed.
by DCT
CPU