Bt8370/8375/8376
3.0 Registers
Fully Integrated T1/E1 Framer and Line Interface
3.6 Primary Control and Status Registers
3.6 Primary Control and Status Registers
Unused bits indicated by a dash (—) are reserved and should be written to 0. Writing to reserved bits has no
effect.
014—Loopback Configuration Register (LOOP)
7
6
5
4
3
2
1
0
—
—
—
—
PLOOP
LLOOP
FLOOP
ALOOP
PLOOP
Enable Remote Payload Loopback—Payload from the receiver replaces the payload on
transmitter output. The loopback payload retains the time slot and frame integrity, so
numbered time slots from each receive frame transfer to same numbered time slots in the
transmit frame. Transmit overhead bits—F-bits in T1 mode or TS0 in E1 mode—are supplied
by the transmit frame formatter or the transmit system bus, according to TFRM [addr 072]
settings. Existing transmit frame alignment and clock timing is not altered by PLOOP
activation or deactivation, allowing system operation with independent receive and transmit
timing. Controlled frame slips are performed in the payload loopback path if the receive and
transmit clocks are asynchronous, although these slips are not reported to the processor as slip
buffer errors. Multiframe integrity is not maintained during PLOOP; therefore, DS0 channel
loopbacks [TPCn; addr 100–11F] must be used to implement payload loopbacks when
transparent or forced signaling is desired. PLOOP does not override by the transmit
per-channel selections (TPCn).
0 = no loopback
1 = payload loopback
LLOOP
Enable Remote Line Loopback—Dual-rail unipolar data from RLIU (or RJAT) is internally
connected to TLIU. The recovered clock from RPLL (or JCLK from RJAT) is internally
connected to the transmitter. Loopback data retains BPV transparency. Data input from the
transmit system bus continues to pass through the transmitter, but is ignored at ZCS encoder
outputs. Data passage from RLIU block to RSB block is unaffected. LLOOP and FLOOP can
be simultaneously active to support line and network loopbacks simultaneously.
0 = no loopback
1 = line loopback
FLOOP
Enable Local Framer Loopback—Dual-rail unipolar data from the transmit ZCS encoder is
internally connected to receive ZCS decoder inputs. The signals from the transmit clock input
(TCKI) is internally connected to the receive clock output (RCKO). Externally applied data on
RTIP/RRING inputs is ignored. XTIP/XRING output data is unaffected. If RCKO is selected
as the TCKI clock source [CMUX; addr 01A], an alternate transmit clock source must be
provided when this loopback is activated. Possible configurations include selecting the TCKI
pin or CLADO as the transmit clock source, or programming the JAT in the transmit direction
and setting JFREE to enable the free-running 10 MHz reference [JAT_CR register; addr 002].
0 = no loopback
1 = framer loopback
N8370DSE
Conexant
3-27
CONEXANT [ CONEXANT SYSTEMS, INC ]
