AT&T 3B2/300 Technical Reference Manual page 279

FUNCTIONAL D E S C R I P T I O N - - - - - - - - - - - - - - - - - - - - - - - - - - -
Input/Output Bus Interrupts
Three Peripheral Interrupt signals are logically OR'ed from all I/0 bus devices (PINT2-0[0]).
Three Peripheral Interrupt Acknowledge (PIAK) signals are daisy-chained through all I/0 bus devices.
PIAKI02-0[0] refers to the input acknowledge signal to a feature card. PIAK002-0[0] refers to the
output acknowledge signal from a feature card.
A feature card connects to only one of these three interrupt levels. PINT2[0] is the highest priority
interrupt of these three interrupts. Peripheral controllers (feature cards) request service from the system
board CPU by asserting a Peripheral Interrupt. The system board CPU acknowledges the request for
service by sending a Peripheral Interrupt Acknowledge Input (PIAK) signal corresponding to the level
of the peripheral interrupt being serviced.
The feature card requesting the interrupt responds to the PIAK by returning a vector and preventing
the acknowledge signal from propagating further down the chain by holding PIAKO inactive. The
acknowledged feature card then asserts a Peripheral Data Acknowledge (PDT ACK[O]) signal to indicate
a valid read of the 1/0 bus. The System Board CPU negates the PIAK in response to the PDTACK.
Error Detection
Two I/0 bus signals are used for fault detection: Peripheral Fail (PFAIL[O]) and Peripheral Fault
(PFLT[O]).
The PFAIL[O] signal is common to all feature cards. The signal is sent to report a card failure of any
kind to the system.
The PFL T[O] signal is sent during a bus transaction by the slave when an erroneous condition, such
as a bus time-out, is detected.
Self-Configuration
The self-configuration feature automatically rebuilds the operating system following changes in the
Equipped Device Table (EDT) when the system is powered up or rebooted. Figure 3-10 shows the
powerup sequence involving self-configuration. Figure 3-11 shows the manual boot sequence involving
self-configuration.
3-26 TECHNICAL REFERENCE MANUAL