K60P100M100SF2RM Datasheet, PDF (1193/1809 Pages) Freescale Semiconductor, Inc – K60 Sub-Family Reference Manual

Chapter 44 10/100-Mbps Ethernet MAC (ENET)
If the frame sent to the MAC from the user application has a size smaller than 60 bytes,
the MAC automatically adds padding bytes (0x00) to comply with the Ethernet minimum
frame length specification. Transmit padding is always performed and cannot be
disabled.
If the MAC is not allowed to append a CRC (TxBD[TC] = 1), the user application is
responsible for providing frames with a minimum length of 64 octets.
44.4.5.2 MAC Address Insertion
On each frame received from the core transmit FIFO interface, the source MAC address
is either:
• Replaced by the address programmed in the PADDR1/2 fields
(ENETn_TCR[ADDINS] = 1)
• Transparently forwarded to the Ethernet line (ENETn_TCR[ADDINS] = 0)
44.4.5.3 CRC-32 generation
The CRC-32 field is optionally generated and appended at the end of a frame.
The CRC polynomial, as specified in the 802.3 standard, is:
• FCS(x) = x³²+ x²⁶+ x²³+ x²²+ x¹⁶+ x¹²+ x¹¹+ x¹⁰+ x⁸+ x⁷+ x⁵+ x⁴+ x²+ x¹+ 1
The 32 bits of the CRC value are placed in the FCS field so that the x³¹ term is the right-
most bit of the first octet. The CRC bits are thus transmitted in the following order: x³¹,
x³⁰,..., x¹, x⁰.
44.4.5.4 Inter-Packet Gap
In full duplex mode, after frame transmission and before transmission of a new frame, an
inter-packet gap (programmed in ENETn_TIPG) is maintained. The minimum IPG can
be programmed between 8 and 27 byte-times (64 and 216 bit-times).
In half duplex mode, the core constantly monitors the line. Actual transmission of the
data onto the network occurs only if it has been idle for a 96-bit time period and any
back-off time requirements have been satisfied. In accordance with the standard, the core
begins to measure the IPG from MII_CRS de-assertion.
K60 Sub-Family Reference Manual, Rev. 6, Nov 2011
Freescale Semiconductor, Inc.
1193