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DS21Q55

12.1 Per-Channel Loopback

The per-channel loopback registers (PCLRs) determine which channels (if any) from the backplane should be replaced with the data from the receive side or in other words, off of the T1 or E1 line. If this loopback is enabled, then transmit and receive clocks and frame syncs must be synchronized. One method to accomplish this would be to tie RCLK to TC LK and RFSYNC to TSYNC. There are no restrictions on which channels can be looped back or on how many channels can be looped back.

Each of the bit position in the PCLRs (PCLR1/PCLR2/PCLR3/PCLR4) represent a DS0 channel in the outgoing frame. When these bits are set to a one, data from the corresponding receive channel will replace the data on TSER for that channel.

Register Name:

PCLR1

Register Description:

Per-Channel Loopback Enable Register 1

Register Address:

4Bh

Bit #

Name

Default

7

6

5

4

3

2

1

0

CH8

CH7

CH6

CH5

CH4

CH3

CH2

CH1

0

0

0

0

0

0

0

0

Bits 0 to 7/Per-Channel Loopback Enable for Channels 1 to 8 (CH1 to CH8). 0 = loopback disabled

1 = enable loopback. Source data fro m the corresponding receive channel

Register Name:

PCLR2

Register Description:

Per-Channel Loopback Enable Register 2

Register Address:

4Ch

Bit #

Name

Default

7

6

5

4

3

2

1

0

CH16

CH15

CH14

CH13

CH12

CH11

CH10

CH9

0

0

0

0

0

0

0

0

Bits 0 to 7/Per-Channel Loopback Enable for Channels 9 to 16 (CH9 to CH16).

0 = loopback disabled

1 = enable loopback. Source data from the corresponding receive channel

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information.

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Maxim DS21Q55 specifications Per-Channel Loopback, PCLR1, PCLR2