T8531-TL-DB Agere Systems, Inc., T8531-TL-DB Datasheet - Page 22

• Manufacturer Part Number: T8531-TL-DB
• Description: Multichannel programmable codec chip set. Dry pack tray.
• Manufacturer: Agere Systems, Inc.

Codec Chip Set
Chip Set Functional Description
(continued)
Start-Up After Internal Reset
Autocalibration
Autocalibration is an analog self-test and trimming pro-
cedure controlled by the DSP core. Sine wave signals
are generated in the receive direction. These signals
are looped back at the analog side of the T8532, and
the return signal amplitudes are measured in the trans-
mit path. This procedure provides on-the-spot fault
coverage of the transmit and receive paths. It also cali-
brates the octal devices by modifying the gain on each
channel. Channel four of the T8532 is the only channel
trimmed at the factory for absolute gain accuracy.
When autocalibration is run, all channels are trimmed
with reference to channel four. That is, the gain on
each channel is adjusted so that its absolute gain is
equivalent to that of the trimmed channel. Performing
trimming in this manner provides channel-to-channel
gain matching of better than 0.01 dB. This is a much
better performance than could be achieved using con-
ventional trimming. Trimmed values are placed in data
storage, and absolute gain values are then modified
accordingly any time the absolute gain register is
changed.
The calibration sequence measures the looped-back
power result and compares it to the calibrated channel.
The trim window is 0.2 dB. If any channel exhibits a
power value which is greater than 0.2 dB, the calibra-
tion procedure sets a failure flag for that channel. Trim-
ming will not be performed on the failed channel, and
the channel’s trimmed gain will be left at 0 dB. The
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(continued)
failed channel, therefore, is left in its previous state and
can still be used. The results of calibration are held in
RAM address 0x07F4 for transmit (pass 1) and 0x07F5
for receive (pass 2). A bit is set high for every failed
channel.
The preceding section discussed the sequence of
instructions that must be followed in order to properly
configure the T8531 for normal operation. The auto-
calibration procedure is mandatory after hardware
reset.
Tone Plant
The following tone plant functions are provided in ROM
code in the T8531 device.
DTMF Transceiver
DTMF generation and detection satisfies LSSGR Sig-
naling for Analog Interfaces GR-506 CORE, section
15.
Caller Line Identification
Called ID transmission is performed as specified in TR-
NWT-000031 (CLASS feature: calling number deliv-
ery).
Call Progress Tones
A call progress tone generator is provided. This tone
generator complies with Telcordia * GR-506-CORE
requirements.
* Telcordia is a trademark of Bell Communications Research, Inc.
Lucent Technologies Inc.
November 2000