CX28394/28395/28398
3.0 Registers
Quad/x16/Octal—T1/E1/J1 Framers
3.7 Primary Control and Status Registers
3.7 Primary Control and Status Registers
014—Loopback Configuration Register (LOOP)
Unused bits are reserved and should be written to 0.
7
6
5
4
3
2
1
0
—
—
—
—
PLOOP
LLOOP
FLOOP
—
PLOOP
Enable Remote Payload Loopback—Payload from receiver replaces payload on transmitter
output. Loopback payload retains time slot and frame integrity, such that numbered time slots
from each receive frame are transferred to the same numbered time slots in the transmit frame.
Transmit overhead bits, Fbits in T1 mode or TS0 in E1 mode, are supplied by transmit frame
formatter or by transmit system bus according to TFRM [addr 072] settings. Existing transmit
frame alignment and clock timing is not altered by PLOOP activation or deactivation, thus
allowing system operation with independent receive and transmit timing. Controlled frame
slips are performed in the payload loopback path if 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. This means that DS0 channel loopbacks
[TPCn; addr 100–11F] must be used to implement payload loopbacks when transparent or
forced signaling is desired. Note that TIDLE (in TPCn) overrides PLOOP.
0 = no loopback
1 = payload loopback
LLOOP
Enable Remote Line Loopback—Received dual-rail unipolar data (RPOSI, RNEGI) is
internally connected to transmit dual-rail unipolar data (TPOSO, TNEGO). The receive clock
must also be looped when LLOP is selected in CMUX [addr 01A]; TXCLK must be set to 01
to select RCKI as the transmit clock. Loopback data retains BPV transparency. Data input
from transmit system bus continues to pass through the transmitter, but is ignored at ZCS
encoder outputs. Received data to RSB block is unaffected. LLOOP and FLOOP can be active
simultaneously to support both line and network loopbacks at the same time.
0 = no loopback
1 = line loopback
FLOOP
Enable Local Framer Loopback—Dual-rail unipolar data from transmit ZCS encoder is
internally connected to receive ZCS decoder inputs. Clock switching is automatic during
FLOOP loopback mode.
0 = no loopback
1 = framer loopback
100054E
Conexant
3-27
CONEXANT [ CONEXANT SYSTEMS, INC ]
