MC9S12NE64V1 Datasheet, PDF (330/554 Pages) Freescale Semiconductor, Inc – MC9S12NE64V1 Data Sheet

Chapter 11 Ethernet Media Access Controller (EMACV1)
Table 11-8. Miscellaneous Fields
Index
0-2
3
4
5
6
7
Field
None
TXBYT
BSLOT
RETX
RANDOM
Reserved
Unit
Read 0s
Bytes
Slot time
Retransmissions
N/A
Reserved
TXBYT — Transmit Frame Byte Counter
This11-bit read-only field indicates the number of bytes of the current frame that have been read from
the transmit buffer by the EMAC transmitter. This register does not include transmitted pad data that
is added to frames if less than the minimum amount of data is transmitted nor the FCS data that is
appended to the end of transmit frames. While sending pause frames with the PAUSE command, this
register is ignored.
BSLOT — Backoff Slot Time Counter
This 10-bit read-only field indicates the number of slot times (512 bit times) in progress during the
backoff delay. This counter clears at the end of backoff delay, which is set by the random algorithm.
The MISC[10] bit reads 0.
RETX — Retransmission Counter
This 4-bit read-only field indicates the current retransmission count if retransmission takes place due
to collision. The MISC[10:4] bits read 0.
RANDOM — Backoff Random Number
This10-bit read-only random number is generated for use by the backoff logic. The value returned
when reading this field is random if the transmitter is enabled. The MISC[10] bit reads 0.
11.4 Functional Description
The EMAC provides a 10/100 Mbps Ethernet media access control (MAC) function and is designed to
connect to a PHY device supporting MII. The EMAC is an 802.3 compliant Ethernet controller specifically
optimized for 8-/16-bit embedded processors. The main components of the EMAC are the receiver,
transmitter, MAC flow control, MII management, and receive and transmit Ethernet buffer interfaces.
11.4.1 Ethernet Frame
In an Ethernet network, information is received or transmitted in the form of a frame. The frame format
used for Ethernet consists of preamble (PA), start frame delimiter (SFD), destination address (DA), source
address (SA), type/length field, data field, and frame check sequence (FCS). See Table 11-9.
Table 11-9. Ethernet Frame Structure
Preamble
7 bytes
Start Frame
Delimiter
1 bytes
Destination
Address
6 bytes
Source
Address
6 bytes
Type/ Length
2 bytes
Data
46 to 1500 bytes
Frame Check
Sequence
4 bytes
MC9S12NE64 Data Sheet, Rev. 1.1
330
Freescale Semiconductor