AT&T 3B2/300 Technical Reference Manual page 508

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INTEL 80C186 Microprocessor
The intelligence of the CM521A Card is provided by an INTEL 80C186, 16-bit microprocessor
operating at 8 MHz. Some of the microprocessor features used for the CM521A Card are described in
the following paragraphs. Figure 3-78 shows the CM521A Differential SCSI Host Adapter Card address
map.
ID/Vector Register
The CM521A Differential SCSI Host Adapter Card ID /Vector Register is a 16-bit register that is
used for two functions. Initially the register contains the 16-bit CM521A 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 CM521A
Card ID code to the high order bits (byte 1) of the ID/Vector Register and waits. The CM521A Card ID
code is Ox 0100. 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 CM521A 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 ]).
FUNCTIONAL DESCRIPTION 3-255