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FW802C Datasheet(PDF) 3 Page - Agere Systems |
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FW802C Datasheet(HTML) 3 Page - Agere Systems |
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3 / 24 page  Data Sheet, Rev. 1 FW802C Low-Power PHY IEEE 1394A-2000 August 2002 Two-Cable Transceiver/Arbiter Device Agere Systems Inc. 3 Description The Agere Systems Inc. FW802C device provides the analog physical layer functions needed to implement a two-port node in a cable-based IEEE 1394-1995 and IEEE 1394a-2000 network. Each cable port incorporates two differential line trans- ceivers. The transceivers include circuitry to monitor the line conditions as needed for determining connec- tion status, for initialization and arbitration, and for packet reception and transmission. The PHY is designed to interface with a link-layer controller (LLC). The PHY requires either an external 24.576 MHz crystal or crystal oscillator. The internal oscillator drives an internal phase-locked loop (PLL), which generates the required 400 MHz reference signal. The 400 MHz reference signal is internally divided to provide the 49.152 MHz, 98.304 MHz, and 196.608 MHz clock signals that control transmission of the outbound encoded strobe and data information. The 49.152 MHz clock signal is also supplied to the associated LLC for synchronization of the two chips and is used for resynchronization of the received data. The powerdown function, when enabled by the PD signal high, stops operation of the PLL and disables all circuitry except the cable-not-active signal circuitry. The PHY supports an isolation barrier between itself and its LLC. When /ISO is tied high, the link interface outputs behave normally. When /ISO is tied low, internal differentiating logic is enabled, and the outputs become short pulses, which can be coupled through a capacitor or transformer as described in the IEEE 1394-1995 Annex J. To operate with bus-keeper isolation, the /ISO pin of the FW802C must be tied high. Data bits to be transmitted through the cable ports are received from the LLC on two, four, or eight data lines (D[0:7]), and are latched internally in the PHY in synchronization with the 49.152 MHz system clock. These bits are combined serially, encoded, and transmitted at 98.304 Mbits/s, 196.608 Mbits/s, or 393.216 Mbits/s as the outbound data-strobe information stream. During transmission, the encoded data information is transmitted differentially on the TPA and TPB cable pair(s). During packet reception, the TPA and TPB transmitters of the receiving cable port are disabled, and the receivers for that port are enabled. The encoded data information is received on the TPA and TPB cable pair. The received data-strobe information is decoded to recover the receive clock signal and the serial data bits. The serial data bits are split into two, four, or eight parallel streams, resynchronized to the local system clock, and sent to the associated LLC. The received data is also transmitted (repeated) out of the other active (connected) cable ports. Both the TPA and TPB cable interfaces incorporate differential comparators to monitor the line states during initialization and arbitration. 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 arbitration to set the speed of the next packet transmission. In addition, the TPB channel monitors the incoming cable common-mode voltage for the presence of the remotely supplied twisted-pair bias voltage. This monitor is called bias-detect. The TPBIAS circuit monitors the value of incoming TPA pair common-mode voltage when local TPBIAS is inactive. Because this circuit has an internal current source and the connected node has a current sink, the monitored value indicates the cable connection status. This monitor is called connect-detect. Both the TPB bias-detect monitor and TPBIAS connect-detect monitor are used in suspend/resume signaling and cable connection detection. The PHY provides a 1.86 V nominal bias voltage for driver load termination. This bias voltage, when seen through a cable by a remote receiver, indicates the presence of an active connection. The value of this bias voltage has been chosen to allow interoperability between transceiver chips operating from 5 V or 3 V nominal supplies. This bias voltage source should be stabilized by using an external filter capacitor of approximately 0.33 µF. The transmitter circuitry, the receiver circuitry, and the twisted-pair bias voltage circuity are all disabled with a powerdown condition. The powerdown condition occurs when the PD input is high. The port transmitter circuitry, the receiver circuitry, and the TPBIAS output are also disabled when the port is disabled, suspended, or disconnected. The line drivers in the PHY operate in a high- impedance current mode and are designed to work with external 112 Ω line-termination resistor networks. One network is provided at each end of each 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 directly connected to the twisted-pair A (TPA) signals is connected to the PBIAS voltage signal. The midpoint of the pair of |
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