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TSB83AA22C Fiches technique(PDF) 4 Page - Texas Instruments |
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TSB83AA22C Fiches technique(HTML) 4 Page - Texas Instruments |
4 / 8 page www.ti.com TSB83AA22C SLLS851 – JUNE 2007 When connected to an IEEE Std 1394a-2000-compliant node, the TSB83AA22C Phy section provides a 1.86-V nominal bias voltage at the TPBIAS terminal for port termination. The Phy section contains two 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 TSB83AA22C Phy section 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 selected 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 TSB83AA22C is off while the twisted-pair cables are connected, the TSB83AA22C transmitter and receiver circuitry present to the cable a high-impedance signal that does not load the device at the other end of the cable. When the TSB83AA22C Phy section 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 port must be forced to the IEEE Std 1394a-2000-only mode (data-strobe-only mode), after which 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 terminal can be connected through a 1- μF capacitor to ground or left unconnected. The TESTM, TESTW, SE, and SM terminals are used to set up various manufacturing test conditions. For normal operation, the TESTM and TESTW terminals must be connected to VDD through a 1-k Ω resistor. The SE and SM terminals must be tied to ground through a 1-k Ω resistor. Three package terminals are used as inputs to set the default value for three configuration status bits in the self-ID packet. They can be pulled high through a 1-k Ω resistor or hardwired low as a function of the equipment design. The PC0, PC1, and PC2 terminals indicate the default power class status for the node (the need for power from the cable or the ability to supply power to the cable). The contender bit in the Phy register set indicates that the node is a contender either for the isochronous resource manager (IRM) or for the bus manager (BM). On the TSB83AA22C, this bit can only be set by a write to the Phy register set. If a node is to be a contender for IRM or BM, then the node software must set this bit in the Phy register set. The LPS (link power status) terminal of the Phy section works with the LKON terminal to manage the power usage in the node. The PHY_LPS signal from the LLC section is used in conjunction with the LCtrl bit (see Table 1 and Table 2 in the APPLICATION INFORMATION section) to indicate the active/power status of the LLC section. The LPS signal also resets, disables, and initializes the Phy section–LLC section interface (the state of the PHY section–LLC section interface is controlled solely by the LPS input regardless of the state of the LCtrl bit). The LPS terminal of the Phy section must be connected to the PHY_LPS terminal of the LLC section during normal operation. The LPS input is considered inactive if it remains low for more than the LPS_RESET time (see the LPS terminal definition) and is considered active otherwise. When the Phy section detects that the LPS input is inactive, the PHY section–LLC section interface is placed into a low-power reset state in which the CTL and D outputs are held in the logic 0 state and the LREQ input is ignored; however, the PCLK output remains active. If the LPS input remains low for more than the LPS_DISABLE time (see the LPS terminal definition), then the Phy section–LLC section interface is put into a low-power disabled state in which the PCLK output is also held inactive. The TSB83AA22C continues the necessary Phy repeater functions required for normal network operation regardless of the state of the Phy section–LLC section interface. When the interface is in the reset or disabled state and the LPS input is again observed active, the Phy section initializes the interface and returns to normal operation. The Phy section–LLC section interface is also held in the disabled state during hardware reset. When the LPS terminal is returned to an active state after being sensed as having entered the LPS_DISABLE time, the TSB83AA22C issues a bus reset. This broadcasts the node self-ID packet, which contains the updated L bit state (the Phy section and LLC section now being accessible). 4 Submit Documentation Feedback |
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Description similaire - TSB83AA22C |
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