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TSB41BA3D データシート(PDF) 3 Page - Texas Instruments |
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TSB41BA3D データシート(HTML) 3 Page - Texas Instruments |
3 / 59 page NOTE: TSB41BA3D www.ti.com ............................................................................................................................................... SLLS959A – DECEMBER 2008 – REVISED MARCH 2009 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 TSB41BA3D 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 TSB41BA3D 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 TSB41BA3D is off while the twisted-pair cables are connected, the TSB41BA3D 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 TSB41BA3D 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. To operate a port as a 1394b bilingual port, the speed/mode selections terminals (S5_LKON, S4, S3, S2_PC0, S1_PC1, and S0_PC2) need to be pulled to VCC or ground through a 1-kΩ resistor. The port must be operated in the 1394b bilingual mode whenever a 1394b bilingual or a 1394b Beta-only connector is connected to the port. To operate the port as a 1394a-only port, the speed/mode selection terminals must be configured correctly to force 1394a-2000-only operation on that port. The only time the port must be forced to the data-strobe-only mode is if the port is connected to a 1394a connector (either 6-pin, which is recommended, or 4-pin). This mode is provided to ensure that 1394b signaling is never sent across a 1394a cable. Copyright © 2008–2009, Texas Instruments Incorporated Submit Documentation Feedback 3 Product Folder Link(s): TSB41BA3D |
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