RTL8208

2001/01/07

13

Rev.1.923

Reset – In order to reset the RTL8208 by software control, a ‘1’ must be written to bit 15 using an SMI write operation. The bit

clears itself after the reset process is complete, and does not need to be cleared using a second SMI write. Writes to other Control

register bits will have no effect until the reset process is completed, which requires approximately 1us. Writing a ‘0’ to this bit

has no effect. Because this bit is self clearing after a few cycles from a write operation, it will return a ‘0’ when read.

Loopback – The RTL8208 may be placed into loopback mode by writing a ‘1’ to bit 14. Loopback mode may be cleared either

by writing a ‘0’ to bit 14 or by resetting the chip. When this bit is read, it will return a ‘1’ when the chip is in software-controlled

loopback mode, otherwise it will return a ‘0’.

Speed Selection – If Auto-negotiation is enabled, this bit has no effect on the speed selection. However, if Auto-negotiation is

disabled by software control, the operating speed of the RTL8208 can be forced by writing the appropriate value to bit 13.

Writing a ‘1’ to this bit forces 100Base-X operation, while writing a ‘0’ forces 10Base-T operation. When this bit is read, it

returns the value of the software controlled forced speed selection only.

Auto Negotiation Enable – Default Auto Negotiation enable for all TP ports and disable for FX ports. Auto-negotiation can be

disabled by either software control to set 0.12=0.

Power Down – The RTL8208 supports a low power mode which is intended to decrease power consumption. Writing a ‘1’ will

enable power down mode, and writing a ‘0’ will return the RTL8208 to normal operation. When read, this register will return a

‘1’ when in power down mode, and a ‘0’ during normal operation.

Isolate – Each individual PHY may be isolated from its MII by writing a ‘1’ to bit 10. All MII outputs will be tri-stated and all

MII inputs will be ignored. Since the MII management interface is still active, the isolate mode may be cleared either by writing

a ‘0’ to bit 10 or by resetting the chip. When this bit is read, it will return a ‘1’ when the chip is in isolate mode, and a ‘0’ during

normal operation.

Restart Auto Negotiation – Bit 9 is a self-clearing bit that allows the Auto-negotiation process to be restarted, regardless of the

current status of the Auto-negotiation state machine. In order for this bit to have an effect, Auto-negotiation must be enabled.

Writing a ‘1’ to this bit restarts Auto-negotiation while writing a ‘0’ to this bit has no effect. When this bit is read, it will always

return a ‘0’.

Duplex Mode – By default, the RTL8208 powers up in half duplex mode. The chip can be forced into full duplex mode by

writing a ‘1’ to bit 8 while Auto-negotiation is disabled. Half duplex mode can be resumed either by writing a ‘0’ to bit 8 or by

resetting the chip. When Nway is enabled, this bit reflects the results of the Auto-negotiation, and is in a read only mode. When

Nway is disabled, this bit can be set through the SMI, and is in a read/write mode. When 100FX is enabled, this bit can be set

through the SMI or FX_DUPLEX pin and is in a read/write mode.

Reserved Bits – All reserved MII register bits must be written as ‘0’ at all times. Ignore the RTL8208 output when these bits are

read.