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CHAPTER 3 INTERRUPTS
3.7 Extended Intelligent I/O Service (EI2OS)
The EI2OS function, a kind of hardware interrupt operation, automatically transfers data
between input and output and memory. An interrupt processing program was
conventionally used for such processing, but EI2OS enables data transfer to be
performed like DMA (direct memory access).
■Extended Intelligent I/O Service (EI2OS)
EI2OS 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 (buffer address is update).
At the end of EI2OS, processing automatically branches to an interrupt processing routine after the end
condition is set. Thus, the user can identify the end condition.
To implement EI2OS, the hardware is distributed in two blocks. Each block has the following registers and
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 outlines the extended intelligent I/O service.