3. STD Bus Interface
ÛZIATECH
31
Non-Maskable Interrupts
As shown in the "
Non-Maskable Interrupt Structure
" figure, the ZT 8907 supports three
sources of non-maskable interrupt requests:
•
STD bus NMIRQ* (P46)
•
AC power-fail detection
•
PCI bus parity error
The STD bus NMIRQ* and AC power-fail interrupts (enabled through jumpers W6 and
W7) combine with the PCI bus parity error interrupt before being routed to the CPU.
Both the STD bus NMIRQ* and AC power-fail interrupts are maskable through port 61h.
Bits 0 and 1 on the Digital I/O ASIC's System Register 2 (E4h) indicate whether a non-
maskable interrupt was generated by the STD bus or an AC power failure. Bit 2 of the
port 61h register indicates whether a non-maskable interrupt was generated by a parity
error.
Non-Maskable Interrupt Structure
CPU
61h
BIT 3
61h
BIT 2
NMI
SOFTWARE
MASK
SOFTWARE
MASK
JUMPER
MASK
JUMPER
MASK
STD BUS
NMIRQ*
PCI
PARITY
AC
DETECT
PORT
PORT
ZT8907
W6
W7
RESET
The ZT 8907 is automatically reset with a precision voltage monitoring circuit that
detects when Vcc is below the acceptable operating limit of 4.75 V. Other sources of
reset include the watchdog timer, local pushbutton switch, and the STD bus pushbutton
reset signal, PBRESET* (P48).
The ZT 8907 responds to any of these reset sources by initializing local peripherals and
driving the STD bus system reset, SYSRESET* (P47). STAR SYSTEM temporary