Datasheet

DS26521 Single T1/E1/J1 Transceiver

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8.9.15 T1 Programmable In-Band Loop Code Generator

The DS26521 can generate and detect a repeating bit pattern from one to eight bits or 16 bits in length. This

function is available only in T1 mode.

Table 8-25. Registers Related to T1 In-Band Loop Code Generator

FRAMER

ADDRESSES

FUNCTION

Transmit Code Definition Register 1

(

T1TCD1)

1ACh Pattern to be sent for loop code.

Transmit Code Definition Register 2

(

T1TCD2)

1ADh Length of the pattern to be sent.

Transmit Control Register 3 (TCR3) 183h

TLOOP bit for control of number of patterns being

sent.

Transmit Control Register 4 (TCR4) 186h Length of the code being sent.

To transmit a pattern, the user loads the pattern to be sent into the Transmit Code Definition registers (T1TCD1

and

T1TCD2) and selects the proper length of the pattern by setting the TC1 and TC0 bits in Transmit Control

TCR4). When generating a 1-, 2-, 4-, 8-, or 16-bit pattern, both T1TCD1 and T1TCD2 must be filled

with the proper code. Generation of a 3-, 5-, 6-, and 7-bit pattern only requires

T1TCD1 to be filled. Once this is

accomplished, the pattern is transmitted as long as the TLOOP control bit (

TCR3.0) is enabled. Normally (unless

the transmit formatter is programmed to not insert the F-bit position) the framer overwrites the repeating pattern

once every 193 bits to allow the F-bit position to be sent.

As an example, to transmit the standard loop-up code for Channel Service Units (CSUs), which is a repeating

pattern of ...10000100001..., set TCD1 = 80h, TC0 = 0, TC1 = 0, and TCR3.0 = 1.