30 www.xilinx.com Virtex-4 RocketIO MGT User GuideUG076 (v4.1) November 2, 2008Preface: About This Guide RPort and Attribute NamesAll input and output ports of the RocketIO transceiver primitives are denoted in upper-case letters. Attributes of the RocketIO transceiver can be denoted in upper-case letterswith underscores or all upper-case letters.When assumed to be the same frequency, RXUSRCLK and TXUSRCLK are referred to asUSRCLK and can be used interchangeably. This also holds true for RXUSRCLK2,TXUSRCLK2, and USRCLK2.Comma DefinitionA comma is a “K” character used by the transceiver to align the serial data on abyte/half-word boundary (depending on the protocol used), so that the serial data iscorrectly decoded into parallel data.Jitter DefinitionJitter is defined as the short-term variations of significant instants of a signal from theirideal positions in time (ITU). Jitter is typically expressed in a decimal fraction of UnitInterval (UI), for example, 0.3 UI.Total Jitter (DJ + RJ) Definition• Deterministic Jitter (DJ) – DJ is data pattern dependant jitter, attributed to a uniquesource (for example, Inter Symbol Interference (ISI) due to loss effects of the media).DJ is linearly additive.• Random Jitter (RJ) – RJ is due to stochastic sources, such as thermal and flicker noise,and so on. RJ is additive as the sum of squares and follows a normal distribution.MGT DefinitionThe term MGT refers to the Virtex-4 RocketIO Multi-Gigabit Transceiver. Previousgenerations are explicitly called out: Virtex-II Pro RocketIO or Virtex-II Pro X RocketIO X.
