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3.7
Extended Intelligent I/O Service (EI
2
The EI
OS function automatically transfers data between input and output and memory.
An interrupt processing program was conventionally used for such processing, but
2
EI
OS enables data transfer to be performed like DMA (direct memory access).
■ Extended Intelligent I/O Service (EI
2
EI
OS has the following advantages over the conventional method:
•
The program size can be small because it is not necessary to write a transfer program.
•
No internal register is used for transfer, eliminating the need for register saving and increasing the
transfer speed.
•
Transfer can be terminated from I/O, preventing unnecessary data from being transferred.
•
The buffer address may either be incremented or left unupdated.
•
The I/O register address may either be incremented or left unupdated.
At the end of EI
condition is set. Thus, the user can identify the end condition.
To implement EI
descriptors.
•
Interrupt control register: Exists in the interrupt controller and indicates the ISD address.
•
Extended intelligent I/O service descriptor (ISD): Exists in RAM and holds the transfer mode, I/O
address, number of transfers, and buffer address.
Figure 3.7-1 shows the outline of extended intelligent I/O service.
2
OS)
2
OS, processing automatically branches to an interrupt processing routine after the end
2
OS, the hardware is distributed in two blocks. Each block has the following registers and
CHAPTER 3 INTERRUPTS
2
OS)
71
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