XRT83SL34 datasheet(32/80 Pages) EXAR

32 / 80 page

XRT83SL34

QUAD T1/E1/J1 SH TRANSCEIVER WITH CLOCK RECOVERY AND JITTER ATTENUATOR

REV. P1.0.8

PRELIMINARY

TRANSMITTER (CHANNELS 0 - 3)

TRANSMIT TERMINATION MODE

In Hardware mode, TXTSEL (Pin 84) can be tied “High” to select internal termination mode for all transmit

channels or tied “Low” for external termination. Individual channel control can be done only in Host mode. In

Host mode, bit 6 in the appropriate register for a given channel is set “High” to select the internal termination

mode for that specific transmit channel, see Table 20, “Microprocessor Register #1, Bit Description,” on

page 46.

For internal termination, the transformer turns ratio is always 1:2. In internal mode, no external resistors are

used. An external capacitor of 0.68

µF is used for proper operation of the internal termination circuitry, see

Figure 11.

EXTERNAL TRANSMIT TERMINATION MODE

By default the XRT83SL34 is set for external termination mode at power up or at Hardware reset.

When external transmit termination mode is selected, the internal termination circuitry is disabled. The value of

the external resistors is chosen for a specific application according to the turns ratio selected by TRATIO (Pin

127) in Hardware mode or bit 0 in the appropriate register for a specific channel in Host mode, see Table 10

and Table 22, “Microprocessor Register #3, Bit Description,” on page 50. Figure 12 is a simplified block

FIGURE 13. SIMPLIFIED DIAGRAM FOR E1 IN EXTERNAL TERMINATION MODE (RXTSEL= 0)

TABLE 8: TRANSMIT TERMINATION CONTROL

TXTSEL

TX TERMINATION

TX TRANSFORMER RATIO

EXTERNAL

1:2.45

INTERNAL

1:2

TABLE 9: TERMINATION SELECT CONTROL

TERSEL1

TERSEL0

TERMINATION

100

Ω

110

Ω

120

Ω

9.1

Ω

9.1

Ω

TTIP

TR IN G

RT IP

RRING

Ω

X R T8 3 S L3 4 LIU

Ω

1 :2.45

1:1

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