VITESSE
SEMICONDUCTOR CORPORATION
Data Sheet
10-Bit Transceiver for Fibre
Channel and Gigabit Ethernet
VSC7123
serial data is retimed, deserialized and output on R(0:9). The parallel data will be captured by the adjoining
protocol logic on the rising edges of RCLK and RCLKN.
If serial input data is not present or does not meet the required baud rate, the VSC7123 will continue to
produce a recovered clock, allowing downstream logic functionality to continue. Under these circumstances,
the RCLK/RCLKN output frequency differ from its expected frequency by no more than +1%.
Word Alignment
The VSC7123 provides 7-bit comma character recognition and data word alignment. Word synchronization
is enabled by asserting ENCDET HIGH. When synchronization is enabled, the receiver examines the recovered
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 characters. It occurs only within special characters, known as K28.1, K28.5 and
K28.7, which are defined for synchronization purposes. Improper alignment of the comma character is defined
as any of the following conditions:
1) The comma is not aligned within the 10-bit transmission character such that R0...R6 = “0011111.”
2) The comma straddles the boundary between two 10-bit transmission characters.
3) The comma is properly aligned but occurs in the received character presented during the rising edge of
RCLK rather than RCLKN.
When ENCDET is HIGH and an improperly aligned comma is encountered, the recovered clock is
stretched (never slivered) so that the comma character and recovered clocks are properly aligned to R(0:9). This
results in proper character and word alignment. When the parallel data alignment changes in response to a
improperly aligned comma pattern, some data which would have been presented on the parallel output port may
be lost. Additionally, the first Comma pattern may also be lost or corrupted. Subsequent data will be output
correctly and properly aligned. When ENCDET is LOW, the current alignment of the serial data is maintained
indefinitely, regardless of data pattern.
When encountering a comma character, COMDET is driven HIGH. The COMDET pulse is presented
simultaneously with the comma character and has a duration equal to the data, or half of an RCLK period. The
COMDET 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 2 and Figure 3. Figure 2 shows the case
when a comma character is detected and no phase adjustment is necessary. Figure 2 illustrates the position of
the COMDET pulse in relation to the comma character on R(0:9). Figure 3 shows the case where the K28.5 is
detected, but it is misaligned so 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.
G52212-0, Rev 4.3
03/25//01
Page 3
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