Intel BFCBASE Data Sheet - Page 15
Electrical Specifications, 2.1 Front Side Bus and GTLREF, 2.2 Decoupling Guidelines
UPC - 735858197373
View all Intel BFCBASE manuals
Add to My Manuals
Save this manual to your list of manuals |
Page 15 highlights
Electrical Specifications 2 Electrical Specifications 2.1 2.2 Front Side Bus and GTLREF Most Intel® Xeon® Processor 7200 Series and 7300 Series FSB signals use Assisted Gunning Transceiver Logic (AGTL+) signaling technology. This technology provides improved noise margins and reduced ringing through low voltage swings and controlled edge rates. AGTL+ buffers are open-drain and require pull-up resistors to provide the high logic level and termination. AGTL+ output buffers differ from GTL+ buffers with the addition of an active PMOS pull-up transistor to "assist" the pull-up resistors during the first clock of a low-to-high voltage transition. Platforms implement a termination voltage level for AGTL+ signals defined as VTT. Because platforms implement separate power planes for each processor (and chipset), separate VCC and VTT supplies are necessary. This configuration allows for improved noise tolerance as processor frequency increases. Speed enhancements to data and address buses have made signal integrity considerations and platform design methods even more critical than with previous processor families. Design guidelines for the processor FSB are detailed in the appropriate platform design guidelines (refer to Section 1.3). The AGTL+ inputs require reference voltages (GTLREF_DATA_MID, GTLREF_DATA_END, GTLREF_ADD_MID and GTLREF_ADD_END) which are used by the receivers to determine if a signal is a logical 0 or a logical 1. GTLREF_DATA_MID and GTLREF_DATA_END are used for the 4X front side bus signaling group and GTLREF_ADD_MID and GTLREF_ADD_END are used for the 2X and common clock front side bus signaling groups. GTLREF_DATA_MID, GTLREF_DATA_END, GTLREF_ADD_MID, and GTLREF_ADD_END must be generated on the baseboard (See Table 2-17 for GTLREF_DATA_MID, GTLREF_DATA_END, GTLREF_ADD_MID and GTLREF_ADD_END specifications). Refer to the applicable platform design guidelines for details. Termination resistors (RTT) for AGTL+ signals are provided on the processor silicon and are terminated to VTT. The on-die termination resistors are always enabled on the processor to control reflections on the transmission line. Intel chipsets also provide on-die termination, thus eliminating the need to terminate the bus on the baseboard for most AGTL+ signals. Some FSB signals do not include on-die termination (RTT) and must be terminated on the baseboard. See Table 2-4 and Table 2-6 for details regarding these signals. The AGTL+ bus depends on incident wave switching. Therefore, timing calculations for AGTL+ signals are based on flight time as opposed to capacitive deratings. Analog signal simulation of the FSB, including trace lengths, is highly recommended when designing a system. Contact your Intel Field Representative to obtain the processor signal integrity models, which includes buffer and package models. Decoupling Guidelines Due to its large number of transistors and high internal clock speeds, the processor is capable of generating large average current swings between low and full power states. This may cause voltages on power planes to sag below their minimum values if bulk decoupling is not adequate. Larger bulk storage (CBULK), such as electrolytic capacitors, supply current during longer lasting changes in current demand by the component, such as coming out of an idle condition. Similarly, they act as a storage well for current when entering an idle condition from a running condition. Care must be taken in the baseboard design to ensure that the voltage provided to the processor Document Number: 318080-002 15