The channel characteristics described above have a clear effect on the PHYs ability to establish a link. Two Fieldbus cables, the Siemens 6XV1830-5EH10 and Belden 3076F, show how insertion loss can affect the maximum cable reach of the DP83TD510. Both cable samples are shielded, single twisted pair Fieldbus cables applicable for process and factory automation.

Figure 4-3 Siemens 6XV1830-5EH10 Cable

The insertion loss profile of Siemens cable shows that it complies with the 10Base-T1L insertion loss profile over 1,000 meters, with violations occurring near 1,200 meters. Table 4-4 demonstrates the DP83TD510 can establish a link through auto-negotiation with this cable up to 1,200 meters.

Figure 4-4 Belden 3076F

The Belden cable does not meet the 10Base-T1L insertion loss profile specification. Note the LSM auto-negotiation signaling at 625kbps suffers from this profile and the DP83TD510 can auto-negotiate up to 260 meters, shown in Table 4-4.

When the limitations of insertion loss at the LSM auto-negotiation rate are removed, the DP83TD510 can achieve greater cable reach. When utilizing the auto-negotiation feature, a DSP ANEG script can be run to achieve the same cable lengths seen in forced mode. The script is described below. This script writes to registers only in MMD 0x1F. If using the USB-2-MDIO tool configure the registers, verify that the Extended Register drop-down is set to Yes.

begin
001F 8000 // hard reset
08A6 04A8 // belden enable & IDX force enable
08A1 0D14 // FAGC disabled
08A4 0180 // FAGC init
08A5 0824 // DEQ offset = 2
08F0 0088 // IDX lim = 8, scaling factor for 7
08A2 7A66 // ADC BO aneg
08A3 0552 // ADC BO aneg
001F 4000 // soft reset
end