Software Patent Institute (IEEE Computer Volume 12 Number 6, Pages 67-73)
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Special Feature: The Intel 8089: An Integrated l/O Processor
K. A. El-Ayat
(Image Omitted: As most mainframe manufacturers have demonstrated, the logical solution to I/O control problems is to deploy intelligent I/O subsystems. Intel's 8089 brings this capability to microcomputer systems.)
The design of I/O subsystems is an integral and important step in computer system design. CPUs and I/O peripherals have generally non-compatible bus and timing requirements - - a fact that can result in sig~uficant degradation in system performance. The logical solution to this problem has been the deployment of an intelligent I/O subsystem which isolates the CPU from the I/O peripherals.l~3 The CPU is therefore free to proceed at full speed with its primary task of internal program processing and data manipulation. Control of all I/O operations is then performed by an I/O processor, an integral part of the I/O subsystem. The CPU maintains supervisory control over the system and issues commands and messages to the I/O processor, which then proceeds with all necessary peripheral control operations to complete the desired I/O transaction. The IIO processor is responsible for device initialization, record selection, I/O transfer, simple data transformation, error checking and retries, and it signals the CPU upon successful completion of the I/O transfer.
(Image Omitted: Intel 8089 device characteristics ALU Width 20 bits Memory addressing
capability 1 M byte .....Addressable l/O ports.....64K Process.....HMOS Clock period.....200 nsec
standard, 125 nsec selected Number of channels.....2 Pins.....40 Supply.....+5V.....I)
(Image Omitted: Conventional and dual--bus microcomputer systems In a conventional microcomputer system the CPU executes application and I/O programs. Availability of a single bus in the system means that CPU, I/O peripherals, and DMA controller share the use of theat bus. Bus is therefore heavily utilized, and high- speed I/O may impede application program execution. In a dual bus microcomputer system with I/O processor, the resphsibility for I/O processing is transferred to an I/O processor, whtich executesI/O programs in parallel with the CPU. All I/O peripherals reside on a local I/O bus, significatnly reducing the load on the main system bus.)
Microprocessors of today Isuch as the Intel 80864) have attained respectable performance levels by innovative architectural and technological advances. However, such advances in microprocessor performance may be seriously overshadowed by the constraints...