AT&T 3B2/300 Technical Reference Manual page 420

- - - - - - - - - - - - - - - - - - - - - - - - - - - FUNCTIONAL DESCRIPTION
INTEL 80186 Microprocessor
The intelligence of the NI card is provided by an INTEL 80186, 16-bit microprocessor operating at
8 MHz. Some of the microprocessor features used for the NI card are described in the following
paragraphs. Figure 3-54 shows the NI card address map.
Input/Output Bus Control
The 1/0 bus control circuitry responds to 1/0 bus and 80186 Microprocessor control signals. Three
major paths are listed below:
• 80186 Microprocessor read or write of the system board main memory
• System board CPU read or write NI card
• Interrupt Acknowledge (PIAK[O]).
The 1/0 bus control circuitry responds to the 1/0 bus and to the 80186 Microprocessor control
signals by selectively enabling the appropriate 1/0 bus signals. In addition, the Bus Abort Feature
(BAF) can be prematurely forced. Certain Peripheral Control and Status Register (PCSR) bits can also
be set when the NI is accessed.
FUNCTIONAL DESCRIPTION 3-167