![](http://datasheet.mmic.net.cn/330000/PM4351_datasheet_16444271/PM4351_444.png)
STANDARD PRODUCT
PM4351 COMET
DATA SHEET
PMC-1970624
ISSUE 10
COMBINED E1/T1 TRANSCEIVER
PROPRIETARY AND CONFIDENTIAL
420
Figure 41
- Diagnostic Digital Loopback
BTIF
BRIF
TX
ELST
RX
ELST
Transmitter
T1-XBAS /
E1-TRAN
Framer
T1-FRMR /
E1-FRMR
TJAT
RJAT
CDRC
XLPG
RLPS
TDAT
TCLKO
TXTIP
TXRING
RXTIP
RXRING
RDAT
RCLKI
BTPCM
BTSIG
BTCLK
BRPCM
BRSIG
BRCLK
Diagnostic Loopback
14.8.4 Per-Channel Loopback
The T1 or E1 payload may be looped back on a per-channel or per-timeslot
basis through the use of the TPSC. If all channels are looped back, the result is
very similar to Payload Loopback. In order for per-channel loopback to operated
correctly, the receive elastic store, RX-ELST, must be bypassed by setting the
RXELSTBYP bit to logic 1 and the backplane receive interface must be set to
clock master by setting the CMODE bit in the BRIF Receive Backplane
Configuration register to logic 0. The LOOP bit must be set to logic 1 in the
TPSC Internal Registers for each channel/timeslot desired to be looped back,
and the PCCE bit in the TPSC Configuration register must be set to logic 1.
When all these parameters are configured, the incoming receive
channels/timeslots selected will overwrite their corresponding outgoing transmit
channels/timeslots; the remaining transmit channels will pass through intact.
Note that because the transmit and receive streams are not superframe aligned,
any robbed-bit signaling in the receive stream will not fall in the correct frame
once looped back and that transmit robbed-bit signaling will overwrite the looped
back channel data if signaling insertion is enabled.