MOTOROLA
Chapter 2. Transmitter
2-11
Ethernet Compliant Applications Modes (COMPAT = High)
The ‘Ack’ bit is asserted when three consecutive matching configuration register values are
received. The auto-negotiate state is complete when three consecutive matching
configuration register values are received with the ‘Ack’ bit set. The transmitter continues
sending auto-negotiate sequences once the auto-negotiate sequence is complete for at least
10 ms.
NOTE
See the state diagram in Figure 37-6 of the IEEE Std.
802.3-2002 specification [4] for a complete description.
2.5.1.2
Ethernet Data Transmission Process
Transmitter operation is controlled by the two input control signals XMIT_x_ENABLE and
XMIT_x_ERR. See Table 3-9 for the complete GMII interface to the MC92603.
When both XMIT_x_ENABLE and XMIT_x_ERR inputs are low, the transmitter
broadcasts IDLE Ordered_sets. Whenever a new series of IDLE Ordered_sets are started,
the first IDLE Ordered_set may be an I1 Ordered_set to correct the running disparity, all
subsequent IDLE Ordered sets will be I2s. The transmitter must be aware of even/oddness.
K28.5 code groups are transmitted as the ‘even’ code group and either D5.6 or D16.2 as the
‘odd’ code group. This even/odd flag is set at initialization and must be maintained since
other events will depend on this even/oddness.
When XMIT_x_ENABLE is raised, the data on the XMIT_x_7 through XMIT_x_0 inputs
is assumed to be the first byte of an 8-byte preamble. The preamble usually consists of 7
consecutive 0x55 code groups followed by a 0xD5 code group. The transmitter replaces the
first 0x55 code group in the preamble with a /S/ Ordered_set to indicate Start_of_Frame.
The MC92603 will support shorter preambles. The minimum preamble size is a single 0x55
code group followed by a 0xD5 code group.
If XMIT_x_ERR is also raised when XMIT_x_ENABLE is raised, then a false carrier is
declared, and a void code groups (/V/) is transmitted.
If XMIT_x_ERR is raised after XMIT_x_ENABLE has been raised and while data is being
transferred, this is a request to transmit an error propagation Ordered_set (/V/) for as many
code groups as long as XMIT_x_ERR remains high.
When a normal End_of_Packet is detected (XMIT_x_ENABLE transitions to low and
XMIT_x_ERR remains low), a single End_of_Packet ordered_set (/T/) is transmitted
followed by at least one Carrier_Extend (/R/) ordered_set. A second Carrier_Extend will
be inserted (if necessary) to complete an even/odd pair. This is then followed by IDLE
ordered_sets to indicate the inter-packet gap. The first /I/ may be either an /I1/ or /I2/,
depending on running disparity.
Summary of Contents for MC92603
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