Intel 440GX manual 3. SET Trace Length Requirements, Motherboard Layout and Routing Guidelines

Motherboard Layout and Routing Guidelines

In the SET topology, the only termination is on the Intel® Pentium® II processor substrate. There is no termination present at the other end of the network. Due to the lack of termination, SET exhibits much more ringback than the dual terminated topology. Extra care is required in SET simulations to make sure that the ringback specs are met under the worst case signal quality conditions.

In addition, since there is only one pull-up resistor per net the rising edge response is substantially degraded when using slow corner buffers. This effect manifests itself as a degraded flight time, which results in a reduced maximum trace length that meets the 100 MHz timing requirements. This loss of design flexibility must be carefully weighed against the cost savings from removing the resistors.

Figure 2-10. Topology for Single Processor Designs With Single-End Termination (SET)

		Intel®
1	L1	440GX
		AGPset
Slot

2.3.5.2SET Trace Length Requirements

Intel has performed sensitivity analysis on the SET topology. The required trace lengths for operation at 100 MHz with the SET topology are based on the sensitivity analysis results, and are listed in Table 2-3. Intel’s SET simulations were performed assuming a four layer system board, so that all traces used the microstrip propagation velocity range. The slower propagation of stripline transmission line structures is not included in the recommendations of Table 2-3.

Table 2-3. SET Trace Length Requirements

Trace	Minimum Length	Maximum Length
L1	1.50”	4.00”

Figure 2-11. Solution Space for Single Processor Designs With Single-End Termination (SET)

					2.5
						SUBSTRATE
					2.0	TRACE LENGTH
						[IN]
					1.5
0.0	1.0	2.0	3.0	4.0	5.0
			L1 [in]

Intel®440GX AGPset Design Guide 2-9