AT&T 3B2/300 Technical Reference Manual page 480

- - - - - - - - - - - - - - - - - - - - - - - - - - - FUNCTIONAL DESCRIPTION
Communications Processing
The ISC card supports a variety of synchronous protocols. This diversity is provided by the 8274
Dual Channel Communications Chip. The 8274 controls two independent, full duplexed channels and
directly supports certain of the RS-232C MODEM control signals. The MODEM control signals not
supported by the 8274 are supported by other components of the ISC and are available to the 80186
Microprocessor on data bits Dll-D08 during a read operation of the 8274 Dual Channel
Communications Chip.
ID/Vector Register
The ISC card ID /Vector Register is a 16-bit register that is used for two functions. Initially the
register contains the 16-bit ISC 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.
The ISC card ID code is Ox 0201.
Page Register
The ISC card uses a 24-bit 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.
FUNCTIONAL DESCRIPTION 3-227