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78P2343-IEL Datasheet(PDF) 5 Page - Teridian Semiconductor Corporation |
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78P2343-IEL Datasheet(HTML) 5 Page - Teridian Semiconductor Corporation |
5 / 37 page 78P2343JAT 3-port E3/DS3/STS-1 LIU with Jitter Attenuator Page 5 of 37 2005 Teridian Semiconductor Corporation Rev 2.2 LINE BUILD-OUT The Line Build-Out (LBO) function controls the transmit amplitude and pulse shape in DS3 and STS-1 modes. The selection of LBO depends on the amount of cable the transmitter is connected to. When less than 225 ft of cable is used, the corresponding LBOx pin or LBO bit should be high. When 225ft or more cable is used the corresponding LBO setting (LBOx pin or LBO bit) should be low. LBO can be controlled either from pins or from register settings, depending on the status of the Register Control bit, REGEN. TRANSMIT ENABLE The TXEN bit in the Mode Control Register controls the transmitter output. When logic zero, the transmitter output is disabled. This feature is used to disable ports as well as to multiplex two or more transceivers to one port. The transmitter of any port can also be disabled by floating the respective LBOx pin, in which case it will also power-down the entire transmitter. See section on the Power-Down Function for more info. TRANSMIT MONITOR The transmit monitor function detects activity on the transmitter output at the LOUTPx and LOUTNx pins. When there is a transmitter fault, in the case of an open or short on the chip, the transformer, or the circuit board, the transmit signal amplitude will be altered. The transmit monitor detects the amplitude of the driven signal. The TXNW signal (bit) goes high when the amplitude of the transmit signal is outside a valid amplitude range. When the signal amplitude is either too high or too low for longer than a specified duration, the TXNW bit goes high (See Transmit Monitor Specifications, pg.28). The TXNW signal can be also used to trigger an interrupt on the INTRx pin when serial interface control is not available. JITTER ATTENUATOR Jitter Attenuation function is provided on-chip. The Jitter Attenuator can be configured to be in the transmit or the receive path. When configured in the transmit path, the input clock at TCLK pin is passed through a very low bandwidth digital PLL. The corresponding transmit data is buffered into a FIFO and clocked out using the de-jittered output clock of the PLL. When configured in the receive path, the recovered clock is passed through the low bandwidth digital PLL, and the corresponding receive data is buffered into the FIFO and clocked out using the de-jittered clock. The Jitter Attenuator can be configured independently for each channel by writing to the Jitter Attenuator Control Register (JACR) as follows: JAEN bit JASL bit Jitter Attenuator Mode 0 X Jitter Attenuator disabled 1 0 Jitter Attenuator configured to be in the receive path 1 1 Jitter Attenuator configured to be in the transmit path When serial interface control is not available, the MSL1 pin is provided for global Jitter Attenuator mode selection. Upon power-up or reset, the state of the MSL1 pin is sensed and mapped into the JAEN and JASL register bits for all channels, representing the appropriate mode of operation. After power-up or reset, the state of the MSL1 pin is ignored. The state of the MSL1 pin, and the corresponding Jitter Attenuator configuration is shown below. MSL1 pin Jitter Attenuator Mode L Jitter Attenuator in receive path H Jitter Attenuator in transmit path Z Jitter Attenuator disabled PLL Bandwidth A PLL response with effectively one pole below 27 Hz is adequate to meet the ETSI TBR24 E3 standards. A PLL response with one pole below 40 Hz is adequate to meet the GR-499 (Cat I) DS3 standards. One of two bandwidths can be selected via register settings. The PLL bandwidth is proportional to the data rate as follows: Line Rate JABW bit PLL Bandwidth (Hz) 0 *13 E3 1 188 0 *17 DS3 1 245 0 20 STS1 1 *283 *The default state of the JABW bit depends on which line-rate is selected through the MSL0 pin. If E3 or DS3 mode is selected, the default state is ‘0’. If STS1 mode is selected, the default state is ‘1’. |
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