3. Theory of Operation
37
Backplane Signals
Interrupts can be output on backplane signals INTRQ*, INTRQ1*, INTRQ2* (CNTL),
INTRQ3*, INTRQ4*, NMIRQ*, or IRQx. These signals are software selectable, tri-state,
logical 0 signals. IRQx is a logical 1 STD 32 slot-specific interrupt signal.
Frontplane Signals
The ZT 8995 frontplane interrupts are tri-state logical 0 signals that are software
selectable for FP3*, FP5*, FP7*, and jumper selectable for FP1* or FP6* when the
ZT 8995 is configured for interrupt level IR15. These frontplane signals can be routed to
the processor board with a frontplane ribbon cable.
Additional information on interrupts can be found in Ziatech's
Application Note #8,
available on Ziatech's web site at
http://ziatech.com/graphics/appn8.pdf
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Reader must be installed on your computer to access this file. You can download the
latest version by clicking "Getting Acrobat Reader" on the Adobe web site at
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Wait States
The ZT 8995 incorporates a wait state generator for STD-80 bus compatibility. The wait
state generator inserts one wait state until the ready signal from the network interface
chip can be asserted. This is required for STD-80 compatible wait state timing and
requires that
W19
and
W16
be inserted.
If an STD 32 compatible CPU provides the equivalent STD bus timing by inserting one
wait state on its own, and can sense wait requests being asserted later in the bus cycle,
W16 can be removed. When W16 is removed, wait states are asserted by the WAITRQ*
signal only as needed by the network interface chip. Ziatech's ZT 8910 can operate with
W16 removed. All other Ziatech CPU boards require that W16 be installed. Removing
W19 will disable all wait state requests and should remain installed.
ETHERNET INTERFACE
The National Semiconductor DP83905 Network Interface Controller is compatible with
IEEE 802.3. This device is a CMOS VLSI device designed to interface with Carrier
Sense Multiple Access/Collision Detection (CSMA/CD) networks, including Twisted-pair
Ethernet (10BaseT), Ethernet (10Base5) and Thin Ethernet (10Base2, Cheapernet). All
Media Access Control (MAC) layer functions are provided for transmission and
reception of data packets.
IEEE 802.3
The term "Ethernet" is also used to describe the publicly available CSMA/CD
specification drafted by the IEEE 802.3 committee, although there are some differences
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