DS26521 datasheet(43/258 Pages) MAXIM

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DS26521 Single T1/E1/J1 Transceiver

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8.9.3

T1 Transmit Synchronizer

The DS26521 transmitter can identify the D4 or ESF frame boundary, as well as the CRC multiframe boundaries

within the incoming NRZ data stream at TSER. The TFM (TCR3.2) control bit determines whether the transmit

synchronizer searches for the D4 or ESF multiframe. Additional control signals for the transmit synchronizer are

located in the TSYNCC register. The latched status bit TLS3.0 (LOFD) is provided to indicate that a loss-of-frame

synchronization has occurred. The real-time bit (LOF) is also provided to indicate when the synchronizer is

searching for frame/multiframe alignment. The LOFD bit can be enabled to cause an interrupt condition on

INTB.

Note that when the transmit synchronizer is used, the TSYNC signal should be set as an output (TSIO = 1) and the

recovered frame-sync pulse will be output on this signal. The recovered CRC-4 multiframe sync pulse is output if

enabled with TIOCR.0 (TSM = 1).

Other key points concerning the E1 transmit synchronizer:

1) The Tx synchronizer is not operational when the transmit elastic store is enabled, including IBO modes.

2) The Tx synchronizer does not perform CRC-6 alignment verification (ESF mode) and does not verify

CRC-4 codewords.

The Tx synchronizer cannot search for the CAS multiframe. Table 8-10 shows the registers related to the transmit

synchronizer.

Table 8-10. Registers Related to the Transmit Synchronizer

FRAMER

ADDRESSES

FUNCTION

Transmit Synchronizer Control Register

(TSYNCC)

18Eh

Resynchronization control for the transmit

synchronizer.

Transmit Control Register 3 (TCR3)

183h

TFM bit selects between D4 and ESF for the

transmit synchronizer.

Transmit Latched Status Register 3

(TLS3)

192h

Provides latched status for the transmit

synchronizer.

Transmit Interrupt Mask Register 3

(TIM3)

1A2h

Provides mask bits for the TLS3 status.

Transmit I/O Configuration Register

(TIOCR)

184h

TSYNC should be set as an output.

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