Cpu And Dma Circuitry - AT&T PC 6300 Service Manual

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SYSTEM OVERVIEW
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CPU and DMA Circuitry
The CPU used with the PC 6300 is the 16-bit Intel 8086-2 (or
equivalent). This microprocessor contains the arithmetic and logic
circuitry to extract program instructions from memory and execute
them one at a time. The 8086-2 operates at a frequency of 8 MHz.
There is a socket on the Motherboard for an optional Numeric
Data Processor (NDP). The NDP is a 16-bit Intel 8087-2 NDP (or
equivalent) that serves as a co-processor attached to the 8086 CPU.
The NDP monitors the 8086 instruction stream and extracts only
the commands intended for the 8087. The 8087 NDP instructions
include a full set of arithmetic functions as well as powerful
exponential, logarithmic, and trigonometric functions.
The DMA circuitry on the Motherboard is constructed of:
• DMA Controller
• DMA Segment Register
• DMA Control Buffer
• DMA Data Buffer
• DMA Address Latches.
The main component of the DMA circuitry is the Intel 8237 DMA
(or equivalent) Controller. The DMA Controller is the device that
generates requests to take over the system bus and transfer
information directly from the I/O peripherals to the system
memory and vice versa. This is necessary when moving blocks of
data rapidly from memory to I/O peripherals.
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