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TSB41BA3A

SLLA224A – JUNE 2006 – REVISED OCTOBER 2006

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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 2-, 4-, or 8-bit parallel streams (depending on 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 TSB41BA3A 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 TSB41BA3A 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 is connected to the TPA terminals is connected to its corresponding TPBIAS voltage terminal. The

midpoint of the pair of resistors that is 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 TSB41BA3A is off while the twisted-pair cables are connected, the TSB41BA3A

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 TSB41BA3A 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 can be left unconnected.

If the port is left in bilingual (Bi) mode, then the TPB+ and TPB– terminals can 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 can 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 smaller resistor.

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