AT&T 3B2/300 Technical Reference Manual page 458

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INTEL 80186 Microprocessor
The intelligence of the PORTS card is provided by an INTEL 80186, 16-bit microprocessor
operating at 8 MHz. Some of the microprocessor features used for the PORTS card are described in the
following paragraphs. Figure 3-64 shows the PORTS card address map.
ID/Vector Register
The PORTS card ID /Vector Register is a 16-bit register that is used for two functions. Initially the
register contains the 8-bit PORTS 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 PORTS card ID code to the high order bits (byte 1) of the
ID/Vector Register and waits. The PORTS card ID code is Ox 03. 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 PORTS 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 0480. Bits 06-00 of the Page Register map to Peripheral Physical
Address bits 23-17 (PP A23-17[1 ]).
FUNCTIONAL DESCRIPTION 3-205