Hi,
Many times the RMII link (on twisted-pair) can not be established. When it does established I probed all 4 pairs of the PMD signals with my scope. The signal peak-to-peak magnitude is good enough. When the link is not established the PMD signals are pulled to 3.3V. My system looks like this,
1) DP83849IVS (on board A) is driving/receiving PMD signals through board B to board C. Ethernet port magnetics, etc. are on board C.
2) The traveling distance of the PMD signals (DP83849IVS to Etherent magnetics) is about 19 inches.
3) We do impedance matching on all 3 PCB boards.
4) I haven't do register configuration to the chip through MDC/MDIO management interface yet. Only reset configuration is done as follows.
{RXD0_A, RXD1_A, RXD0_B, RXD1_B}=0000 // PHYAD[4:1]=0000
{AN_EN, AN1, AN0}=111 // Auto-negotiation enabled
MII_MODE_A, SNI_MODE_A}=10 // RMII enabled on port A
{MII_MODE_B, SNI_MODE_B}=10 // RMII enabled on port B
{LED_CFG_A, LED_CFG_B}=00 // LED_CFG[1]=1 is configured only through register access
LED_LINK_A/B: ON for Good Link; BLINK for Activity
LED_SPEED_A/B: ON in 100M/s; OFF in 10Mb/s
LED_ACT/LED_COL_A/B: ON for Full Duplex; OFF for Half Duplex
{MDIX_EN_A, MDIX_EN_B}=11 // MDIX is enabled on port A & B
{ED_EN_A, ED_EN_B}=00 // Energy detect disabled
EXTENDER_EN=1 // extender mode is enabled on port A & B
CLK2MAC_DIS=1 // Clock to MAC output disabled
///// PMD Interface Signals /////
Port A: TPTDP_A, TPTDM_A, TPRDP_A, TPRDM_A
Port B: TPTDP_B, TPTDM_B, TPRDP_B, TPRDM_B
My questions:
1) Does anyone have any idea about where the problem (RMII link having difficulty to establish) might be?
2) If distance is one of the issue please recommend line buffer/repeater for the PMD interface signals.
Thanks a lot.
David