Revision 1.02 – April 12, 2007
S5920 – PCI Product: Signal Description
Data Book
Signal Type Definitions
The following signal types are taken from the PCI Bus Specification.
in
Input is a standard input-only signal.
out
t/s
Totem Pole Output is a standard active driver.
Tri-State ®is a bi-directional, tri-state input/output pin.
s/t/s
Sustained Tri-State is an active low tri-state signal owned and driven by one and only one agent at a time. The
agent that drives an s/t/s pin low must drive it high for at least one clock before letting it float. A new agent cannot
start driving an s/t/s signal any sooner than one clock after the previous owner tri-states it. A pull-up is required to
sustain the inactive state until another agent drives it, and must be provided by the central source.
o/d
Open Drain allows multiple devices to share as a wire-OR.
Each signal that assumes the logic low state when asserted is followed by the pound sign (#). Example: TRDY# signal is
asserted low when the target is ready to complete a data transfer. Signals that are not followed by the pound sign are
asserted when they assume the logic high state.
The following designations are used throughout this book when referring to the size of data objects:
A BYTE is an 8-bit object.
A WORD is a 16-bit, or 2-byte object.
A DWORD is a double word and is a 32-bit or 4-byte object.
All hex numbers are followed by an “h”. Examples:
9A4Fh
0110h
All binary numbers are followed by an “b”. Examples:
1010b
0110b
All decimal numbers are followed by an “d”. Examples:
4356d
1101d
Note: Tri-State® is a Registered Trademark of National Semiconductor.
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