MC68EN360AI25VL Freescale, MC68EN360AI25VL Datasheet - Page 559

• Manufacturer Part Number: MC68EN360AI25VL
• Manufacturer: Freescale

Specifications of MC68EN360AI25VL

• Family Name: M68000
• Device Core: ColdFire
• Device Core Size: 32b
• Frequency (max): 25MHz
• Instruction Set Architecture: RISC
• Operating Supply Voltage (max): 3.3V
• Operating Supply Voltage (min): 2.7V
• Operating Temp Range: 0C to 70C
• Operating Temperature Classification: Commercial
• Mounting: Surface Mount
• Pin Count: 240
• Package Type: FQFP
• Lead Free Status / RoHS Status: Compliant

7.10.22 RAM Microcodes
Additional protocols may be added in the future through the use of RAM microcodes. See
Appendix C RISC Microcode from RAM for more information.
7.10.23 Ethernet Controller
The Ethernet/IEEE 802.3 protocol is a widely used LAN that is based on the carrier sense
multiple access/collision detect (CSMA/CD) approach. Ethernet and IEEE 802.3 frames are
very similar and can co-exist on the same LAN. The two protocols are referred to synony-
mously as "Ethernet" in this manual unless specifically noted. Ethernet/IEEE 802.3 frames
are based on the frame structure shown in Figure 7-65.
The frame begins with a 7-byte preamble of alternating ones and zeros. Since the frame is
Manchester encoded, the preamble gives receiving stations a known pattern on which to
lock. The start frame delimiter, which signifies the beginning of the frame, follows the pre-
amble. The 48-bit destination address is next, followed by the 48-bit source address. Origi-
nal versions of the IEEE 802.3 specification allowed 16-bit addressing; however, this
addressing has never been significantly used in the industry.
The next field is the type field in Ethernet and the length field in IEEE 802.3. The type field
is used to signify the protocol used in the rest of the frame (e.g., TCP/IP). The length field is
used to specify the length of the data portion of the frame. For Ethernet and IEEE 802.3
frames to co-exist on the same LAN, the length field of the frame must always be unique
from any type fields used in Ethernet. This has limited the length of the data portion of the
frame to 1500 bytes, and therefore the total frame length to 1518 bytes.
The final 4 bytes of the frame are the FCS. This is the standard 32-bit CCITT-CRC polyno-
mial used in many other protocols.
When a station wishes to transmit, it checks for activity on the LAN. When the LAN becomes
silent for a specified period, the station begins transmission. During transmission, the station
continually checks for collision on the LAN. If a collision is detected, the station forces a jam
of all ones on its frame and ceases transmission. Collisions usually occur close to the begin-
ning of a frame. The station then waits a random period of time (backoff) before attempting
to transmit again. Once the backoff is complete, the station waits for silence on the LAN and
NOTE: The LSB of each octet is transmitted first.
PREAMBLE
7 BYTES
a busy (out-of-buffers) condition since only one Rx BD was pre-
pared.
DELIMITER
1 BYTE
FRAME
START
Figure 7-65. Ethernet/802.3 Frame Format;
Freescale Semiconductor, Inc.
For More Information On This Product,
6 BYTES
ADDR.
DEST.
MC68360 USER’S MANUAL
Go to: www.freescale.com
SOURCE
6 BYTES
ADDR.
2 BYTES
LENGTH
TYPE/
FRAME LENGTH IS 64–1518 BYTES
Serial Communication Controllers (SCCs)
46–1500 BYTES
DATA
SEQUENCE
4 BYTES
CHECK
FRAME