DM9000A
APPLICATION NOTES
Preliminary 38
Version: DM9000A-AN-V121
November 27, 2007
6.5 AUTO-MDIX and Application circuit
When design AUTO-MDIX circuit of the DM9000A in the embedded system, the following
layout guide must be cared: Traces routed from RXI± and TXO± to the transformer should run
in close pairs directly to the transformer such as YCL-PH163539. The network interface
should be void of any signals other than the TXO± and RXI± pairs between the RJ-45 to the
transformer and the transformer to the DM9000A.
Figure 6.1 AUTO-MDIX 10Base-T/100Base-TX Application.
The DM9000A is default turning on AUTO-MDIX feature, and there are two ways to disable
AUTO-MDIX function:
1. To set the SROM Word 7, Wake-up Mode Control, Bit [14] = 1 then zero to re-load it,
srom_write (0x07, 0x180); /* PHY power-on but disable Auto-MDIX setting into SROM */
iow ( 0x0B, 0x20 );
/* REEP Bit [5] of EPCR REG. 0BH to re-load EEPROM value */
iow ( 0x0B, 0x00 );
/* REEP Bit [5]= 0 normal after 400 us delay for re-load */
2. To write high "1" to the Bit [4] Mdix-down in the PHY REG. 20,
phy_write(20, 0x0010);/* Mdix_down Bit[4]= 1 with Mdix_fix_Value Bit[5]=0 for MDI */
phy_write(20, 0x0030);/* Mdix_down Bit[4]=1 with Mdix_fix_Value Bit[5]=1 for MDIX */
