MC9S12NE64_06 Datasheet, PDF (332/554 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 11 Ethernet Media Access Controller (EMACV1)
hexadecimal string F0-4E-77-8A-35-1D is equivalent to the following sequence of bits, sent over the
network from left to right:
0000 1111 0111 0010 1110 1110 0101 0001 1010 1100 1011 1000
If the LSB of the most-significant byte of the destination address field is a 0, the address field contains an
individual (unicast) address. If the LSB is a 1, the address field contains a group (multicast) address that
identifies none, one or more, or all network nodes connected. There is a special case of the multicast
address known as the broadcast address, which is the 48-bit address of all 1s.
11.4.1.3 Type/Length Field
This 16-bit field takes one of two meanings depending on its numeric value and is transmitted and received
with the high order byte first.
If the value in this field is numerically equal-to or less-than the maximum data size in bytes of 1500
decimal (0x05DC hex), the field is being used as a length field. In this case, the value in the field indicates
the number of bytes contained in the subsequent data field of the frame. When receiving this type frame,
a compare of the value in the type/length field is made to the actual number of bytes received in the data
field of the frame and an error is reported if there is not an exact match.
If the value in this field is numerically greater-than or equal-to 1536 decimal (0x0600 hex), the field is
being used as a type field. In this case, the hexadecimal identifier in the field is used to indicate the type of
protocol data being carried in the data field of the frame. For example, the hexadecimal value of 0x0800
has been assigned as the identifier for the Internet protocol (IP). When receiving this type frame, no
comparison of the value in the type/length field is made to the actual number of bytes received in the data
field of the frame.
If the value in this field is between 1501 and 1535, this frame is invalid but is not automatically rejected.
When receiving this type frame, no comparison of the value in the type/length field is made to the actual
number of bytes received in the data field of the frame.
When transmitting, if the length of the data field is less than the minimum required for the data field of the
frame, bytes of pad data are automatically added at the end of the data field but before the FCS field to
make the data field meet the minimum length requirement. The content of pad data is all 0s. Upon
reception of a frame, the length field stored in the receive buffer is used to determine the length of valid
data in the data field, and any pad data is discarded by software.
11.4.1.4 Data Field
This field must contain a minimum of 46 bytes of data, and may range up to a maximum of 1500 bytes of
data.
11.4.1.5 Frame Check Sequence
This 32-bit field contains the value that is used to check the integrity of the various bits in the frame fields
excluding the preamble and SFD. This value is computed using the cyclic redundancy check (CRC), which
is a polynomial calculated using the contents of the destination address, source address, type/length, and
data fields.
MC9S12NE64 Data Sheet, Rev. 1.1
332
Freescale Semiconductor