
LXT9785 and LXT9785E Advanced 8-Port 10/100 Mbps PHY Transceivers
Datasheet
157
Document Number: 249241
Revision Number: 010
Revision Date: 30-May-2006
When a long event (such as duplex status) occurs, it is edge detected and starts the stretch timer.
When the stretch timer expires, the edge detector is reset so that a long event causes another pulse
to be generated from the edge detector. The edge detector resets the stretch timer, causing the LED
4.12.3
Out-of-Band Signaling
The LXT9785/LXT9785E provides an out-of-band signaling option to transfer status information
across the RMII receive interface. This feature is enabled when Register bit 25.0 = 1 and uses the
RxData(1:0) data bus during the Inter-Packet Gap (IPG) time as shown in
Figure 32. Out-of-Band
signaling is disabled when Isolate mode is enabled by setting Register 0.10.
Note:
The BGA15 package does not support Out-of-Band Signaling nor the RMII interface.
The two status bits transferred across the RxData bus are software selectable via Register 25 (see
In normal operation, the LXT9785/LXT9785E stuffs the RxData bus with zeros during the IPG. A
software-selectable bit enables the RMII out-of-band signaling feature. Once this bit is set, the
LXT9785/LXT9785E replaces the zeros with selected status bits during the IPG.
Figure 31. LED Pulse Stretching
Event
LED
Note: The direct drive LED outputs in this diagram are shown as active L ow.
stretch
Figure 32. RMII Programmable Out-of-Band Signaling
RE FCLK
CRS_DV
RXD(1)
RXD(0)
data
sta tu s 0
status 0
statu s 0
sta tu s 1
status 1
statu s 1
0s
status 1
statu s 0
0s
1. When network activity is detected, the LXT9785/LXT9785E asserts CRS_DV asynchronously with respect
to REFCLK.
2. After CRS_DV is asserted, the LXT9785/LXT9785E zero-stuffs the RxData bits until the received data has
been processed through the FIFO.
3. When network activity ceases, the LXT9785/LXT9785E de-asserts CRS_DV synchronously with respect
to REFCLK. CRS_DV toggles until all data in the FIFO has been processed through the RMII. Once the
FIFO is empty, LXT9785/LXT9785E drives the status bits selected by the Out-of-Band Signaling Register