AT&T 3B2/300 Technical Reference Manual page 472

- - - - - - - - - - - - - - - - - - - - - - - - - - - FUNCTIONAL DESCRIPTION
ID/Vector Register
The XDC card ID /Vector Register is a 16-bit register that is used for two functions. Initially the
register contains the 16-bit XDC card ID code. Later the register contains an 8-bit interrupt vector. The
interrupt vector is returned in response to an Interrupt Acknowledge (PIAK[O]) signal. On reset, the
80186 Microprocessor writes the XDC card ID code to the ID /Vector Register and waits. The XDC card
ID code is Ox 0204. 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 are a unique
16-bit ID code of the card.
Page Register
The XDC card uses a 24-bit
1/0
address to do system board 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 3-219