am79761 Advanced Micro Devices, am79761 Datasheet - Page 10

• Manufacturer Part Number: am79761
• Description: Physical Layer 10-bit Transceiver For Gigabit Ethernet Gigaphy ?d
• Manufacturer: Advanced Micro Devices

Word Alignment
The Am79761 device provides 7-bit comma character
recognition and data word alignment. Word synchroni-
zation is enabled by asserting EN_CDET HIGH. When
synchronization is enabled, the Am79761 device con-
stantly examines the serial data for the presence of the
Comma character. This pattern is 0011111XXX, where
the leading zero corresponds to the first bit received.
The comma sequence is not contained in any normal
8B/10B coded data character or pair of adjacent char-
acters. It occurs only within special characters, known
as K28.1, K28.5, and K28.7, which are defined specifi-
cally for synchronization purposes. Improper alignment
of the comma character is defined as any of the follow-
ing conditions:
1. The comma is not aligned within the 10-bit trans-
2. The comma straddles the boundary between two
3. The comma is properly aligned but occurs in the re-
When EN_CDET is HIGH and an improperly aligned
comma is encountered, the internal data is shifted in
such a manner that the comma character is aligned
10
COM_DET
Note : TChar = 10-bit Transmission Character
mission character such that TXD0...TXD6 =
“0011111.”
10-bit transmission characters.
ceived character presented during the rising edge
of RCLK rather than RCLKN.
RXD[0:9]
RCLKN
RCLK
Figure 18. Detection of a Properly Aligned Comma Character
P R E L I M I N A R Y
K28.5
Am79761
TChar
properly in RXD[0:9]. This results in proper character
and half-word alignment. When the parallel data
alignment changes in response to an improperly
aligned comma pattern, some data which would have
been presented on the parallel output port may be
lost. However, the synchronization character and
subsequent data will be output correctly and properly
aligned. When EN_CDET is LOW, the current align-
ment of the serial data is maintained indefinitely,
regardless of data pattern.
When encountering a comma character, COM_DET is
driven HIGH to inform the user that realignment of the
parallel data field may have occurred. The COM_DET
pulse is presented simultaneously with the comma char-
acter and has a duration equal to the data, or half of an
RCLK period. The COM_DET signal is timed such that it
can be captured by the adjoining protocol logic on the
rising edge of RCLKN. Functional waveforms for
synchronization are given in Figure 18 and Figure 19.
Figure 18 shows the case when a comma character is
detected and no phase adjustment is necessary. It illus-
trates the position of the COM_DET pulse in relation to
the comma character on RXD[0:9]. Figure 19 shows the
case where K28.5 is detected, but it is out of phase and
a change in the output data alignment is required. Note
that up to three characters prior to the comma character
may be corrupted by the realignment process.
TChar
TChar
21560A-4