VSC7216

Multi-Gigabit Interconnect Chip

Multi-Gigabit Interconnect Chip

Preliminary Data Sheet

VSC7216-01

VITESSE

SEMICONDUCTOR CORPORATION

Page 4

G52352-0, Rev 3.2

05/05/01

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Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: prodinfo@vitesse.com

Internet: www.vitesse.com

When used, the TBCn inputs must be frequency-locked to REFCLK. No phase relationship is assumed. A

small skew buffer is provided to tolerate phase drift between TBCn and REFCLK. This buffer is recentered by

the RESETN input, and the total phase drift after recentering must be limited to ±180

° (where 360° is one

character time). Each channel has an error output, TBERRn, that is asserted HIGH to indicate that the phase

drift between TBCn and REFCLK has accumulated to the point that the elastic limit of the skew buffer has been

exceeded and a transmit data character has been either dropped or duplicated. This error can not occur when

input timing is referenced to REFCLK. The TBERRn output timing is identical to the low-speed receiver

outputs, as selected by RMODE(1:0) in Table 6.

Figures 2 through 4 show the possible relationships between data and control inputs and the selected input

timing source. Figure 2 shows how REFCLK is used as an input timing reference. This mode of operation is

used in the VSC7211 and VSC7214. Figure 3 and Figure 4 show how TBCn is used as an input timing

reference. When TBCn is used to define a data eye as shown in Figure 4, it functions as an additional data input

that simply toggles every cycle.

Note that the REFCLK and TBCn inputs are not used directly to clock the input data. Instead, an internal

Phase-Lock Loop (PLL) generates edges aligned with the appropriate clock. The arrows on the rising edges of

these signals define the reference edge for the internal phase detection logic. An internal clock is generated at

one-tenth the serial transmit data rate that is locked to the selected input timing source. This is an especially

important issue when DUAL is HIGH and input timing is referenced to REFCLK, since the falling edge is NOT

used. The internal clock active edges are placed coincident with the REFCLK rising edges and halfway between

the REFCLK rising edges in this mode.

A similar situation exists when TBCn is used to define a data eye, only the rising edges of TBCn are used to

define the external data timing. The internal clock active edges are placed at 90

° and 270° points between

consecutive TBCn rising edges (which are assumed to be 360

° apart).

Figure 2: Transmit Timing, TMODE(2:0) = 000

Figure 3: Transmit Timing, TMODE(2:0) = 10X

REFCLK

(DUAL = 0)

Valid

C/Dn

Valid

Valid

Tn(7:0)

WSENn

REFCLK

(DUAL = 1)

Valid

C/Dn

Valid

Valid

Tn(7:0)

WSENn

or

TBCA

TBCn