LXT9785 and LXT9785E Advanced 8-Port 10/100 Mbps PHY Transceivers
Datasheet
Document Number: 249241
Revision Number: 007
Revision Date: August 28, 2003
163
Link Hold-Off software control is enabled or disabled on individual ports by respectively setting or
clearing Register bit 0.11, the power-down bit, during normal operation. It is not required to have
previously enabled Link Hold-Off by hardware configuration.
Link Hold-Off is disabled if the external pin MDDIS is active. The MDDIS pin disables the MDIO
interface required to re-enable normal transmit and receive link operation. MDDIS is intended to
disable the MDIO management interface for unmanaged applications. Internal loopback circuitry
is unaffected in Link Hold-Off mode.
4.14.2
Operation
Link Hold-Off is implemented in one of the following two ways:
Using a hardware pin at power-up or hardware reset
Using software control through the MII Management (MDC/MDIO) interface.
Link Hold-Off use by an external hardware pin is as follows:
1. Pull the LINKHOLD pin High with a pull-up resistor (approximately 5 k Ohms).
2. Power up the system or drive the reset pin active.
3. All ports are link disabled.
4. Program all ports to the desired configuration.
5. Clear Register Bit 0.11, power-down for each individual port.
6. Normal operation resumes on each port after Register bit 0.11 is cleared (see Table 83 for the
recovery time).
Link Hold-Off is enabled on a per port basis by software control using the following two methods:
Method One:
This method requires that Link Hold-Off is enabled by the LINKHOLD pin during the last power-
up or hardware reset.
1. Set Register bit 0.15 to reset and re-enable Link Hold-Off for the desired port.
2. Program the PHY to the desired configuration.
3. Clear Register bit 0.11 (power-down) to disable Link Hold-Off.
4. Normal operation resumes.
Method Two:
This method enables Link Hold-Off regardless of the LINKHOLD hardware configuration state.
1. Set Register bit 0.11(power-down) to enable Link Hold-Off for the desired port.
2. Program the PHY to the desired configuration.
3. Clear Register bit 0.11 (power-down) to disable Link Hold-Off.
4. Normal operation resumes.
Note:
High is defined by the IO voltage supply level selected (2.5V or 3.3V).