TSB41BA3 datasheet(3/63 Pages) TI

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TSB41BA3

IEEE 1394b THREEPORT CABLE TRANSCEIVER/ARBITER

SLLS155A − MAY 2003 − REVISED OCTOBER 2003

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

description (continued)

NOTE:

The BMODE terminal does not select the cable interface mode of operation. The BMODE terminal

selects the PHY-link interface mode of operation and affects the arbitration modes on the cable.

When the BMODE terminal is deasserted, the PHY-link interface is placed in 1394a-2000 mode and

BOSS arbitration is disabled. When the BMODE terminal is asserted, the PHY-link interface is

placed in 1394b-2002 mode and BOSS arbitration is enabled.

During packet reception the serial data bits are split into two-, four-, or eight-bit parallel streams (depending upon

the indicated receive speed and the PHY-link interface mode of operation), resynchronized to the local system

clock and sent to the associated LLC. The received data is also transmitted (repeated) on the other connected

and active cable ports.

Both the twisted pair A (TPA) and the twisted pair B (TPB) cable interfaces incorporate differential comparators

to monitor the line states during initialization and arbitration when connected to a 1394a-2000 compliant device.

The outputs of these comparators are used by the internal logic to determine the arbitration status. The TPA

channel monitors the incoming cable common-mode voltage. The value of this common-mode voltage is used

during 1394a-mode arbitration and sets the speed of the next packet transmission. In addition, the TPB channel

monitors the incoming cable common-mode voltage on the TPB pair for the presence of the remotely supplied

twisted pair bias (TPBIAS) voltage.

When connected to a 1394a-2000 compliant node, the TSB41BA3 provides a 1.86-V nominal bias voltage at

the TPBIAS terminal for port termination. The PHY contains three independent TPBIAS circuits (one for each

port). This bias voltage, when seen through a cable by a remote receiver, indicates the presence of an active

connection. This bias voltage source must be stabilized by an external filter capacitor of 1

µF.

The line drivers in the TSB41BA3, are designed to work with external 112-

Ω termination resistor networks in

order to match the 110-

Ω cable impedance. One termination network is required at each end of a twisted-pair

cable. Each network is composed of a pair of series-connected ~56-

Ω resistors. The midpoint of the pair of

resistors that are connected to the TPA terminals is connected to its corresponding TPBIAS voltage terminal.

The midpoint of the pair of resistors that are directly connected to the TPB terminals is coupled to ground through

a parallel RC network with recommended values of 5 k

Ω and 270 pF. The values of the external line-termination

resistors are designed to meet the standard specifications when connected in parallel with the internal receiver

circuits. A precision external resistor connected between the R0 and R1 terminals sets the driver output current,

along with other internal operating currents.

When the power supply of the TSB41BA3 is off while the twisted-pair cables are connected, the TSB41BA3

transmitter and receiver circuitry present a high-impedance signal to the cable that does not load the device at

the other end of the cable.

When the TSB41BA3 is used without one or more of the ports brought out to a connector, the twisted-pair

terminals of the unused ports must be terminated for reliable operation. For each unused port, the preferred

method is for the port to be forced to the 1394a-only mode (data-strobe-only mode, DS), then the TPB+ and

TPB– terminals can be tied together and then pulled to ground; or the TPB+ and TPB– terminals can be

connected to the suggested normal termination network. The TPA+ and TPA– terminals of an unused port can

be left unconnected. The TPBIAS#_SD# terminal may be left unconnected.

If the port is left in bilingual (Bi) mode, then the TPB+ and TPB– terminals may be left unconnected or the TPB+

and TPB– terminals can be connected to the suggested normal termination network. The TPA+ and TPA–

terminals of an unused port can be left unconnected. The TPBIAS#_SD# terminal can be left unconnected.

If the port is left in a forced 1394b beta only (B1, B2, or B4) mode, then the TPB+ and TPB– terminals may be

left unconnected or the TPB+ and TPB– terminals can be connected to the suggested normal termination

network. The TPA+ and TPA– terminals of an unused port can be left unconnected. The TPBIAS#_SD# terminal

must be pulled to ground through a 1.2-k

Ω or less resistor.

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