CN8380 Datasheet, PDF (42/91 Pages) Conexant Systems, Inc – integrated quad line interface unit unit for both 1.544 Mbps (T1) and 2.048 Mbps (E1) applications

2.0 Circuit Description
2.5 Loopbacks
CN8380
Quad T1/E1 Line Interface
2.5 Loopbacks
Three per-channel loopbacks are provided for system diagnostic testing: Local
Analog Loopback, Local Digital Loopback, and Remote Line Loopback.
Loopbacks can be controlled by either hardware pins or internal register bits. For
hardware control, two dedicated pins—LLOOP and RLOOP—are provided. If
configured in Host Mode, register bits are provided for loopback control. In
addition, the LLOOP and RLOOP pins can be enabled by register bits so that
loopbacks can be controlled by the hardware pins even in Host Mode. Loopback
controls are detailed in Table 2-9. Refer also to register LIU_CTL [addr n3] in
Chapter 3.0, Registers.
Table 2-9. Loopback Control Pins
LLOOP
RLOOP
Loopback
1
1
None
1
0
Remote Line Loop
0
1
Local Analog Loop
0
0
Local Digital Loop
2.5.1 Local Analog Loopback
Local Analog Loopback (LAL) causes the transmit data and clock inputs
(TPOSI/TNEGI and TCLK) to be looped back to the receiver outputs
(RPOSO/RNEGO and RCKO). This loopback connects an internal copy of the
analog transmit signal (XTIP and XRING outputs) to the receiver input, so that
virtually all of the device circuitry can be tested. While LAL is active, transmit
data continues to be transmitted on XTIP and XRING, but RTIP and RRING
inputs are ignored. Applying a high on the XOE pin when Local Analog Loopback
is active disables the transmitter outputs and causes an RLOS.
2.5.2 Local Digital Loopback
Local Digital Loopback (LDL) causes the transmit data and clock inputs
(TPOSI/TNEGI and TCLK) to be looped back to the receiver outputs
(RPOSO/RNEGO and RCKO). This loopback includes the JAT (if enabled) but
does not include the line transmit and receive circuitry. Consequently, XTIP and
XRING transmitter outputs are unaffected, and receiver RTIP and RRING inputs
remain connected to the line to monitor for RLOS. Also, the AIS (all 1s)
generator is not included in the loopback path so that AIS can be transmitted
toward the line while simultaneously providing a local loopback.
2-20
Conexant
N8380DSA
Advance Information