Intel 21555 Signal Nomenclature, Signal Type Abbreviations, Signal Description Type, Sts

Preface

1.4Signal Nomenclature

21555 device signal names are printed in lowercase type. Prefixes and suffixes are tagged with a leading or trailing letter and are delimited with an “_” underscore:

•The prefix “p_” denotes a primary bus signal. For example: p_ad is the primary interface address/data bus.

•The prefix “s_” denotes a secondary bus signal. For example: s_ad is the secondary interface address/data bus.

•Other prefixes might appear. l_(load), pr_(parallel rom), and so on.

•The suffix “_l” means that the condition is qualified when that signal is low or approximately zero (0) volts. For example: p_frame_l is a low-asserted signal.

•If no suffix is applied, it means that the condition is qualified when the signal is high or approximately equal to vcc. For example: p_idsel is a high-asserted signal.

PCI signals that can be on either the primary interface or the secondary interface are printed in uppercase, normal type. The names of low-asserted signals are followed by #. For example, “asserting FRAME#” can refer to the assertion of the p_frame_l signal when the transaction is occurring on the primary bus or the assertion of the s_frame_l signal when the transaction is occurring on the secondary bus.

Table 1 describes the Signal Type letters that appear in Table 6 through Table 10 in Chapter 3, “Signal Descriptions”.

Table 1. Signal Type Abbreviations

Signal	Description
Type
I	Standard input only.
O	Standard output only.
TS	Tristate bidirectional.
STS	Sustained tristate. Active low signal must be pulled high for one clock
	cycle when deasserting.
OD	Standard open drain.

21555 Non-Transparent PCI-to-PCI Bridge User Manual 13