Datasheet

DS26518 8-Port T1/E1/J1 Transceiver

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9.9.15 T1 Programmable In-Band Loop Code Generator

The DS26518 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 9-33. Registers Related to T1 In-Band Loop Code Generator

FRAMER 1

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.

Note: The addresses shown above are for Framer 1. Addresses for Framers 2 to 8 can be calculated using the following: Framer n = (Framer 1

address + (n - 1) x 200hex), where n = 2 to 8 for Framers 2 to 8.

To transmit a pattern, the user will load the pattern to be sent into the Transmit Code Definition Registers (T1TCD1

and

T1TCD2) and select the proper length of the pattern by setting the TC0 and TC1 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 will be 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 will overwrite 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.