Acer S2W 3300U Service Manual - Page 27

5.2.3 Data Signaling Data transmission within a packet is done with differential signals. A differential 1 on the bus is represented by D+ being at least 200mV positive than D- as seen at the receiver, and a differential 0 is represented by D- being st least 200 mV more positive than D+ as seen st the receiver. The signal cross over point must be between 1.3 V and 2.0V. The start of a packet (SOP) is signaled by the originating port by divinig the D+ and D- lines from the idle state to opposite logic level (K state). This switch in levels represents the first bit of the Sync field. Hubs must limit the distortion of the width of the first bit after SOP when it is retransmitted to less than 5 ns. Distortion can be minimized bymatching the nominal data delay through the hub with the output enable delay of the hub. The single-ended 0 state is used to signal an end of packet (EOP). The single-ended 0 state is indicated by both D+ and D- being below 0.8V. EOP will be signaled by driving d+ and D- to the single-ended 0 state for two bit times followed by driving the lines to the idle state for one bit time. The transition from the single-ended 0 o the idle state defines the end of the packet. The idle state is asserted for 1 bit time and then both the D+ and Doutput drivers are placed in their high-impedance state. The bus termination resistors hold the bus in the idle state. Figure 5-23 shows the signaling for start and end of a packet.