Intel X3370 INXEON3370 Data Sheet

22

Datasheet

Overshoot events on processor must meet the specifications in 

 when 

measured across the VCC_SENSE and VSS_SENSE lands. Overshoot events that are < 

10 ns in duration may be ignored. These measurements of processor die level 

overshoot must be taken with a bandwidth limited oscilloscope set to a greater than or 

equal to 100 MHz bandwidth limit.

Most processor Front Side Bus signals use Gunning Transceiver Logic (GTL+) signaling 

technology. This technology provides improved noise margins and reduced ringing 

through low voltage swings and controlled edge rates.

 

Platforms implement a 

termination voltage level for GTL+ signals defined as V

TT

. Because platforms implement 

separate power planes for each processor (and chipset), separate V

CC

 and V

TT 

supplies 

are necessary. This configuration allows for improved noise tolerance as processor 

frequency increases. Speed enhancements to data and address busses have caused 

signal integrity considerations and platform design methods to become even more 

critical than with previous processor families. Design guidelines for the processor front 

side bus are detailed in the appropriate platform design guides (refer to 

).

The GTL+ inputs require a reference voltage (GTLREF) which is used by the receivers to 

determine if a signal is a logical 0 or a logical 1. GTLREF must be generated on the 

 for GTLREF specifications). Refer to the applicable 

platform design guidelines for details. Termination resistors (R

TT

) for GTL+ signals are 

provided on the processor silicon and are terminated to V

TT

. Intel chipsets will also 

provide on-die termination, thus eliminating the need to terminate the bus on the 

motherboard for most GTL+ signals.

The front side bus signals have been combined into groups by buffer type. GTL+ input 

signals have differential input buffers, which use GTLREF[3:0] as a reference level. In 

this document, the term “GTL+ Input” refers to the GTL+ input group as well as the 

GTL+ I/O group when receiving. Similarly, “GTL+ Output” refers to the GTL+ output 

group as well as the GTL+ I/O group when driving. 

With the implementation of a source synchronous data bus comes the need to specify 

two sets of timing parameters. One set is for common clock signals which are 

dependent upon the rising edge of BCLK0 (ADS#, HIT#, HITM#, etc.) and the second 

set is for the source synchronous signals which are relative to their respective strobe 

lines (data and address) as well as the rising edge of BCLK0. Asychronous signals are 

still present (A20M#, IGNNE#, etc.) and can become active at any time during the 

clock cycle. 

 identifies which signals are common clock, source synchronous, 

and asynchronous.