K60P100M100SF2RM Datasheet, PDF (1224/1809 Pages) Freescale Semiconductor, Inc – K60 Sub-Family Reference Manual

Functional Description
44.4.16 FIFO Protection
The following sections describe the FIFO protection mechanisms.
44.4.16.1 Transmit FIFO Underflow
During a frame transfer, when the transmit FIFO reaches the almost empty threshold with
no end-of-frame indication stored in the FIFO, the MAC logic:
• Stops reading data from the FIFO
• Asserts the MII error signal (MII_TXER) (1) to indicate that the fragment already
transferred is not valid
• Deasserts the MII transmit enable signal (MII_TXEN) to terminate the frame transfer
(2)
After an underflow, when the application completes the frame transfer (3), the MAC
transmit logic discards any new data available in the FIFO until the end of packet is
reached (4) and sets the enhanced TxBD[UE] bit.
The MAC starts to transfer data on the MII interface when the application sends a new
frame with a start of frame indication (5).
Transmit FIFO
TX CLK
TX ready
FIFO data
section empty
Write enable
Start of packet
End of packet
TX data
TX error status
4
3
MII Transmit
MII_TXCLK
MII_TXEN
MII_TXD[3:0]
55
55
MII_TXER
1
2
5
Figure 44-66. Transmit FIFO Underflow Protection
1224
K60 Sub-Family Reference Manual, Rev. 6, Nov 2011
Freescale Semiconductor, Inc.