APPLICATION NOTE 3111

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


Abstract: The DS3144 has four independent DS3/E3 framers on a single die and includes all necessary circuitry to frame and format four separate DS3 or E3 channels. Each framer in this device is independently configurable to support M23 DS3, DS3 C-Bit Parity, or G.751 frame formats with all applicable alarm detection and generation. The DS3144 interfaces to a variety of line interface units (LIUs), microprocessor buses, and other system components without glue logic. The digital data interface to the LIU can be Binary (NRZ) or Bipolar (POS/NEG), and provides internal B3ZS/HDB3 encoders and decoders. The DS3154 quad LIU performs the functions necessary for interfacing at the physical layer to DS3, E3, or STS-1 lines. Each LIU has an independent receive and transmit path and a built-in jitter attenuator. Each port of the DS3154 is independently configurable. The DS3154 has both hardware or CPU bus configuration options.

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

DS3/E3 Framer Description
DS3141 Single-Port Framer
DS3142 Dual-Port Framer
DS3143 Triple-Port Framer
DS3146 6-Port Framer
DS3148 8-Port Framer
DS31412 12-Port Framer
DS3/E3/STS-1 LIU Description
DS3151 Single-Port LIU
DS3152 Dual-Port LIU
DS3153 Triple-Port LIU

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.

Table 1. Line Interface Register Map for DS3144

ADDR. REGISTER BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
01h MC1 LOTCMC ZCSD BIN MECU AECU TUA1 DISABLE RST
02h MC2 OSTCS TCCLK N/A N/A N/A DLB LLB PLB
03h MC3 TDENMS TSOFC TOHENI TOHI TSOFI TICLKI TDATI TDENI
04h MC4 RDENMS ROOFI RLOSI RDATH RSOFI ROCLKI RDATI RDENI
05h MC5 RNEGI RPOSI RCLKI TNEGH TPOSH TNEGI TPOSI TCLKI
06h ISR1 N/A N/A N/A N/A INT4 INT3 INT2 INT1
08h MSR LORC LOTC T3E3 FEAC HDLC BERT COVF N/A
09h MSRL LORCL LOTCL N/A N/A N/A N/A COVFL OSTL
OAh MSRIE LORCIE LOTCIE T3E3IE FEACIE HDLCIE BERTIE COVFIE OSTIE

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.

Table 2. DS3/E3 Framer Register Map for DS3144

ADDR. REGISTER BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
10 T3E3CR1 E3SnC1 E3SnC0 T3IDLE TRAI TAIS TPT CBEN DS3M
11 T3E3CR2 FRESYNC N/A TFEBE AFEBED ECC FECC1 FECC0 E3CVE
12 T3E3EIC MEIMS FBEIC1 FBEIC0 FBEI T3CPBEI T3PBEI EXZI BPVI
18 T3E3SR N/A N/A SEF T3IDLE RAI AIS OOF LOS
19 T3E3SRL COFAL N/A SEFL T3IDLEL RAIL AISL OOFL LOSL
1A T3E3SRIE COFAIE N/A SEFIE T3IDLEIE RAIIE AISIE OOFIE LOSIE
1B T3E3IR RUA1 T3AIC E3Sn N/A EXZL MBEL FBEL ZSCDL
20 BPVCR1 BPV7 BPV6 BPV5 BPV4 BPV3 BPV2 BPV1 BPV0
21 BPVCR2 BPV15 BPV14 BPV13 BPV12 BPV11 BPV10 BPV9 BPV8
22 EXZCR1 EXZ7 EXZ6 EXZ5 EXZ4 EXZ3 EXZ2 EXZ1 EXZ0
23 EXZCR2 EXZ15 EXZ14 EXZ13 EXZ12 EXZ11 EXZ10 EXZ9 EXZ8
24 FECR1 FE7 FE6 FE5 FE4 FE3 FE2 FE1 FE0
25 FECR2 FE15 FE14 FE13 FE12 FE11 FE10 FE9 FE8
26 PCR1 PE7 PE6 PE5 PE4 PE3 PE2 PE1 PE0
27 PCR2 PE15 PE14 PE13 PE12 PE11 PE10 PE9 PE8
28 CPCR1 CPE7 CPE6 CPE5 CPE4 CPE3 CPE2 CPE1 CPE0
29 CPCR2 CPE15 CPE14 CPE13 CPE12 CPE11 CPE10 CPE9 CPE8
2A FEBECR1 FEBE7 FEBE6 FEBE5 FEBE4 FEBE3 FEBE2 FEBE1 FEBE0
2B FEBECR2 FEBE15 FEBE14 FEBE13 FEBE12 FEBE11 FEBE10 FEBE9 FEBE8

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.

Table 3. Register Map for DS3154

ADDR. REGISTER BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
00h GCR1 E3M STS LLB RLB TDSA TDSB - RST
01h TCR1 - TBIN TCINV TJA TPD TTS TLBO -
02h RCR1 ITU RBIN RCINV RJA RPD RTS RMON RCVUD
03h SR1 - - TDM PRBS - - RLOL RLOS
04h SRL1 - - TDML PRBSL PBERL RCVL RLOLL RLOSL
05h SRIE1 - - TDMIE PRBSIE PBERIE RCVIE RLOLIE RLOSIE
06h RCVL1 RCV[7] RCV[6] RCV[5] RCV[4] RCV[3] RCV[2] RCV[1] RCV[0]
07h RCVH1 RCV[15] RCV[14] RCV[13] RCV[12] RCV[11] RCV[10] RCV[9] RCV[8]
O8h-0Fh TEST - - - - - - - -

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 Maxim framer DS3144 and the Maxim LIU DS3154.

Figure 1. Functional diagram for the framer and LIU.
Figure 1. Functional diagram for the framer and LIU.

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 Maxim framers and LIUs, please contact the Maxim Telecommunications applications support team.