AT&T 3B2/300 Technical Reference Manual page 502

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INTEL 80186 Microprocessor
The intelligence of the EPORTS card is provided by an INTEL 80186, 16-bit microprocessor
operating at 8 MHz. Some of the microprocessor features used for the EPORTS card are described in
the following paragraphs. Figure 3-76 shows the EPORTS card address map.
ID/Vector Register
The EPORTS card ID/Vector Register is a 16-bit register that is used for two functions. Initially the
register contains the 16-bit EPORTS card ID code. Later the register contains an 8-bit interrupt vector
for the ID code. The interrupt vector is returned in response to an Interrupt Acknowledge (PIAK[O])
signal. On reset, the 80186 Microprocessor writes the EPORTS card ID code to the high order bits
(byte 1) of the ID/Vector Register and waits. The EPORTS card ID code is Ox 0102. During system
self-configuration, the system board CPU polls each feature card slot. This polling reads the ID /Vector
Register. The two bytes of the ID/Vector Register form a unique 16-bit ID code of the card.
Page Register
The EPORTS card uses a 24-bit 1/0 address to do main memory operations. The lower 17 bits are
provided by the 80186 Microprocessor. The most significant 7 bits are provided by the Page Register.
The Page Register is a write only register for the 80186 Microprocessor. The two most significant
address bits (bits 06 and 05) of the Page Register are always zero. This allows the Page Register to
select thirty-two 128 kilobyte segments of main memory. The Page Register is addressed by the 80186
Microprocessor at its 1/0 address Ox 0482. Bits 06-00 of the Page Register map to Peripheral Physical
Address bits 23-17 (PP A23-17[1 ]).
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