psf21911 ETC-unknow, psf21911 Datasheet - Page 77

• Manufacturer Part Number: psf21911
• Description: Isdn Echocancellation Circuit Terminal Applications Iec-q
• Manufacturer: ETC-unknow

PSB 21911
PSF 21911
U-Transceiver
Complete loop-back
The complete loop-back comprises both B-channels and the D-channel. It may be closed
either in the U-transceiver itself , in the S-transceiver or in an external device.
When receiving the EOC-command LBBD in EOC auto mode, the U-transceiver does
not close the loop-back immediately. Because the intention of this loop-back is to test the
complete NT, the U-transceiver passes the complete loop-back request on to the IOM-2
interface. This is achieved by issuing the C/I-code AIL in the “Transparent” state or C/I =
ARL in states different than “Transparent”. In applications that include a microcontroller,
the software decides where to close the loop, whereas in an NT1 the loop is closed
automatically in the S-transceiver (e.g. SBCX).
Single-channel loop-back (B1/B2)
Single-channel loop-backs are always performed directly in the U-transceiver if EOC
auto mode is selected. No difference between the B1-channel and the B2-channel loop-
back control procedure exists. They are therefore discussed together.
The B1-channel is closed with the EOC-command LB1. LB2 causes the channel B2 to
loop-back. Because these functions are latched, both channels may be looped back
simultaneously by sending first the command to close one channel followed by the
command for the remaining channel.
2.5.9.2
Analog Loop-Back (No. 3)
Loop-back #3 is invoked by sending C/I command ARL to the U-transceiver. The loop is
closed by the U-transceiver as near to the U-interface as possible. For this reason it is
also called analog loop-back. All analog signals will still be passed on to the U-interface.
As a result the opposite station (LT) is activated as well.
In order to open an analog loop-back correctly, reset the U-transceiver into the TEST
state with the C/I-command RES. This ensures that the echo coefficients and equalizer
coefficients will converge correctly when activating the following time.
Semiconductor Group
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