Interfacing the DS3144 Framer with the DS3154 Line Interface Unit (LIU)

This application note also applies to the following Analog framers with Analog LIUs:

DS3144 Receive-Framer LIU-Interface Pins

Receive Positive Data Input/Receive NRZ Data Input (RPOS/RNRZ): If BIN = 0 in the MC1 register, the LIU interface is in bipolar (POS/NEG) mode. In this mode, the framer clocks in the serial data stream in AMI format. RPOS = 1 from an external LIU indicates a positive pulse was received on the line; RNEG = 1 from the LIU indicates a negative pulse was received on the line. If BIN = 1, the framer is in binary (NRZ) LIU-interface mode. In this mode the framer clocks in the serial data stream in binary format on the RNRZ pin. RNRZ = 1 indicates a 1 in the data stream; RNRZ = 0 indicates a 0 in the data stream.

Receive Negative Data Input/Receive Line-Code Violation Input (RNEG/RLCV): If BIN = 0 in the MC1 register, the LIU interface is in bipolar (POS/NEG) mode. In this mode, the framer clocks in the serial data stream in alternate-mark inversion (AMI) format. RPOS = 1 from an external LIU indicates a positive pulse was received on the line, while RNEG = 1 from the LIU indicates a negative pulse was received on the line. If BIN = 1, the framer is in binary (NRZ) LIU interface mode. In this mode the framer clocks in the serial data stream in binary format on the RNRZ pin and line-code violations on the RLCV pin.

Receive Clock Input (RCLK): RCLK is used to clock data into the receive framer on RPOS/RNEG (bipolar LIU interface mode) or RNRZ (binary LIU interface mode). If RCLKI = 0 in the MC5 register, data is clocked into the framer on the rising edge of RCLK. If RCLKI = 1, data is clocked in on the falling edge of RCLK. RCLK is normally accurate to within ±20ppm when sourced from an LIU, but the framer can also accept a gapped clock up to 52MHz on RCLK, such as those commonly soured from ICs that map/demap DS3 and E3 to/from SONET/SDH.

DS3144 Transmit-Formatter LIU-Interface Pins

Transmit Positive Data Output/Transmit NRZ Data Output (TPOS/TNRZ): If BIN = 0 in the MC1 register, the LIU interface is in bipolar (POS/NEG) mode. In this mode, the transmit formatter outputs the serial data stream in AMI format. TPOS = 1 signals an external LIU to drive a positive pulse on the line, while TNEG = 1 tells the LIU to drive a negative pulse on the line. If BIN = 1, the LIU interface is in binary (NRZ) mode. In this mode, the transmit formatter outputs the serial data stream in binary format on the TNRZ pin. TNRZ = 1 indicates a 1 in the data stream, while TNRZ = 0 indicates a 0.

Transmit Negative Data Output (TNEG): If BIN = 0 in the MC1 register, the LIU interface is in bipolar (POS/NEG) mode. In this mode, the transmit formatter outputs the serial data stream in AMI format. TPOS = 1 signals an external LIU to drive a positive pulse on the line, while TNEG = 1 tells the LIU to drive a negative pulse on the line. If BIN = 1, the LIU interface is in binary (NRZ) mode. In this mode the transmit formatter outputs the serial data stream in binary format on the TNRZ pin, and TNEG is driven low.

Transmit Clock Output (TCLK): TCLK is used to clock data out of the transmit formatter on TPOS/TNEG (bipolar LIU interface mode) or TNRZ (binary LIU interface mode). If TCLKI = 0 in the MC5 register, data is clocked out of he formatter on the rising edge of TCLK. If TCLKI = 1, data is clocked out on the falling edge of TCLK. TCLK is normally a buffered (and optionally inverted) version of TICLK. When either line loopback or payload loopback is active, TCLK is a buffered (and optionally inverted) version of RCLK. When a clock is not present on TICLK and MC1:LOTCMC = 1, TCLK is a buffered (and optionally inverted) version of RCLK.

DS3154 Receive-LIU Framer-Interface Pins

Receiver Positive AMI/Receiver Data (RPOS/RDAT): When the receiver is configured to have a bipolar interface (RBIN = 0), RPOS pulses high for each positive AMI pulse received. When the receiver is configured to have a binary interface (RBIN = 1), RDAT outputs decoded binary data. RPOS/RDAT is updated either on the falling edge of RCLK (RCINV = 0) or the rising edge of RCLK (RCINV = 1).

Receiver Negative AMI/Line-Code Violation (RNEG/RLCV): When the receiver is configured to have a bipolar interface (RBIN = 0), RNEG pulses high for each negative AMI pulse received. When the receiver is configured to have a binary interface (RBIN = 1), RLCV pulses high to flag code violations. RNEG/RLCV is updated either on the falling edge of RCLK (RCINV = 0) or the rising edge of RCLK (RCINV = 1).

Receiver Clock (RCLK): The recovered clock is output on the RCLK pin. Recovered data is output on the RPOS/RDAT and RNEG/RLCV pins on the falling edge of RCLK (RCINV = 0) or the rising edge of RCLK (RCINV = 1). During a loss of signal (RLOS = 0), the RCLK output signal is derived from the LIU's master clock.

DS3154 Transmit-LIU Framer-Interface Pins

Transmitter Positive AMI/Transmitter Data (TPOS/TDAT): When the transmitter is configured to have a bipolar interface (TBIN = 0), a positive pulse is transmitted on the line when TPOS is high. When the transmitter is configured to have a binary interface (TBIN = 1), the data on TDAT is transmitted after B3ZS or HDB3 encoding. TPOS/TDAT is sampled either on the rising edge of TCLK (TCINV = 0) or on the falling edge of TCLK (TCINV = 1).

Transmitter Negative AMI (TNEG): When the transmitter is configured to have a bipolar interface (TBIN = 0), a negative pulse is transmitted on the line when TNEG is high. When the transmitter is configured to have a binary interface (TBIN = 1), TNEG is ignored and should be wired either high or low. TNEG is sampled either on the rising edge of TCLK (TCINV = 0) or on the falling edge of TCLK (TCINV = 1).

Transmitter Clock (TCLK): A DS3 (44.736MHz _20ppm), E3 (34.368MHz _20ppm), or STS-1 (51.840MHz _20ppm) clock should be applied at this signal. Data to be transmitted is clocked into the device at TPOS/TDAT and TNEG either on the rising edge of TCLK (TCINV = 0) or the falling edge of TCLK (TCINV = 1).

Registers of the DS3144 and the DS3154 Required for the Interface

Table 1 shows the DS3144 registers that are responsible for top-level configuration, control, and status of each framer, including resets, clocks, pin controls, and line-interface function.

Note: Bits that are underlined are read-only bits. Bits that are marked N/A are undefined. Undefined bits are reserved for future enhancements and must always be written with logic 0 and ignored when read.

Table 2 shows the DS3144 DS3/E3 framer registers. In this register map, underlined bits are for read-only. Bits that are marked N/A are undefined. Undefined bits are reserved for future enhancements and must always be written with logic 0 and ignored when read.

These registers in Table 2 are responsible for top-level configuration, control, and status of each framer on DS3 and E3 mode.

The DS3154 can operate in either hardware mode or CPU bus mode.

In hardware mode, pulling the input pins high or low does all configurations. All the status information is reported on status output pins. Internal registers are not accessible in hardware mode. The device is configured for hardware mode when the HW pin is wired high (HW = 1).

In CPU bus mode, most of the configuration and status pins used in hardware mode are reassigned to be address, data, and control lines that interface to an 8-bit microprocessor bus. The device is configured for CPU bus mode when the HW pin is wired low (HW = 0).

With the exception of the HW pin, configuration and status pins available in hardware mode have corresponding register bits in the CPU bus mode. The hardware mode pins and the CPU bus mode register bits have identical names and functions, with the exception that all register bits are active high. Table 3 shows the register map of DS3154, which can be used for the interface with DS3144.

Implementing the Interface Between the Framer and LIU

The DS3144 device will always have power-on reset enabled. After reset, all read/write control register bits are reset to 0 except for RDATH and TUA1, which are set to 1. Complete operation details for the reset of this device is available in the DS3144 data sheet. The DS3144 needs to be configured for either DS3 or E3 after resetting the device. In all modes, the TUA1 bit in the MC1 register and RDATH bit in the MC4 register must be cleared. These bits are set to 1 at reset to generate an unframed all-ones (E3 AIS) signal on both the transmit LIU interface (TPOS/TNEG) and the receive system interface (RDAT).

After reset the default LIU interface format of DS3144 is bipolar (POS/NEG) with B3ZS/HDB3 encoding and decoding enabled. To change framer operation after reset to binary (NRZ) format with B3ZS/HDB3 encoding and decoding disabled (disabled in the framer but should be enabled in the LIU), BIN bit needs to be set to 1 in the MC1 register.

Framer Interface Format and the B3ZS/HDB3 Decoder for DS3154

The data can be output in either binary or bipolar format. To select the bipolar interface format, the RBIN pin needs to be low in hardware mode. In CPU bus mode, the RBIN configuration bit needs to be cleared.

In bipolar format, the B3ZS/HDB3 decoder is disabled and the recovered data is buffered and output on the RPOS and RNEG outputs. Received positive-polarity pulses are indicated by RPOS = 1, while negative-polarity pulses are indicated by RNEG = 1.

In bipolar interface format, the receiver simply passes on the received data and does not check it for BPV or EXZoccurrences. To select the binary interface format, the RBIN pin needs to be high in hardware mode. In CPU bus mode, the RBIN configuration bit needs to be set.

In binary format, the B3ZS/HBD3 decoder is enabled, and the recovered data is decoded and output as a binary value on the RDAT pin. Code violations are flagged on the RLCV pin.

To support interface to a variety of neighboring components, the polarity of RCLK can be inverted. Normally, data is output on the RPOS/RDAT and RNEG/RLCV pins on the falling edge of RCLK. To output data on these pins on the rising edge of RCLK, the RCINV pin needs to be pulled high in hardware mode or the RCINV configuration bit needs to be set in CPU bus mode.

The RCLK, RPOS/RDAT, and RNEG/RLCV pins can be tri-stated to support protection switching and redundant-LIU applications. This tri-stating capability supports system configurations where two or more LIUs are wire-ORed together and a system processor selects one to be active. To tri-state RCLK, RPOS/RDAT, and RNEG/RLCV, assert the RTS pin or the RTS configuration bit. Figure 1 shows the functional diagram for the Analog framer DS3144 and the Analog LIU DS3154.

Conclusion

For more help on designing the hardware for the interface between framer and LIU, refer to the DS3144DK data sheet.

For further questions about the operations of and/or the interface between Analog framers and LIUs, please contact the Analog Tech Support Team.