Bt8370/8375/8376
2.0 Circuit Description
2.11 Loopbacks
Fully Integrated T1/E1 Framer and Line Interface
2.11.4 Local Analog Loopback
RLIU provides a local analog loopback to internally route bipolar data from
XTIP/XRING to RTIP/RRING. In the local analog loopback mode, externally
applied data on RTIP/RRING inputs is ignored, and XTIP/XRING output data is
unaffected. The local analog loopback is configured using the ALOOP bit in the
Loopback Configuration register [LOOP; addr 014]. 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]. After activating or deactivating
this loopback, the RLIU must be reset using RST_LIU in the LIU Configuration
register [LIU_CR; addr 020]. The transmitter outputs must connect to a cable
termination or a transmit termination resistor for local analog loopback to pass
bipolar signals. If no cable and no resistor termination are supplied, then ALOOP
cannot pass bipolar signals to RTIP/RRING.
2.11.5 Local Framer Loopback
The local framer loopback loops the transmit line encoder outputs to the receive
line encoder inputs. The TLIU output is not affected by the activation of this
loopback. The local framer loopback is activated by setting the Local Framer
Loopback (FLOOP) bit in the Loopback Configuration register [LOOP;
addr 014]. If RCKO is selected as the TCKI clock source [CMUX; addr 01A],
then 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]. It is possible to operate the local framer loopback simultaneously with
the remote line loopback. If transmit jitter attenuator is also enabled, TJAT is
placed in the framer loopback path. RJAT, if enabled, is not present in the framer
loopback path.
2.11.6 Local Per-Channel Loopback
The local per-channel loopback loops the TSB PCM and signaling inputs to the
RSB PCM and signaling outputs on a per-channel basis. The local per-channel
PCM loopback is activated by setting RLOOP in the System Bus Per-Channel
Control registers [SBC0 to SBC31; addr 0E0 to 0FF]. The local per-channel
signaling loopback is activated by setting SIG_LP in System Bus Per-Channel
Control registers.
N8370DSE
Conexant
2-87
CONEXANT [ CONEXANT SYSTEMS, INC ]
