PCI-X electrical and mechanical features

This chapter discusses the electrical signaling aspects of peripheral component interconnect (PCI)-X and reviews that PCI-X mode-1 uses a 3.3 volt signaling environment similar to PCI 66. The timing requirements are naturally tighter for PCI-X 133. Mode-2 uses a new 1.5 volt signaling environment for category 1 signals. Mostly, 1.5V receivers require termination that must be switchable. In source synchronous mode, an initiator generates the strobe signals that clock data into the target. This minimizes the problems of propagation delay because the data and strobes are following the same path and thus, have the same delay. System board and add-in card capabilities are determined by the signals PCIXCAP and MODE-2, where intermediate values on PCIXCAP represent PCI-X 66, 266 and 533. PCI-X uses the same basic mechanics as conventional PCI. Additional requirements relate to clearly identifying system boards and add-in cards capable of PCI-X operation.