10
Am79Q4457/5457 Data Sheet
FUNCTIONAL DESCRIPTION
The QSLAC-NP device performs the Codec/Filter and
two-to-four-wire conversion function (requires external
balance impedance) required of the subscriber line in-
terface circuitry in telecommunications equipment.
These functions involve converting an audio signal into
digital PCM samples and converting digital PCM sam-
ples back into an audio signal. During conversion, dig-
ital filters are used to band limit the voice signals. All of
the digital filtering is performed in digital signal proces-
sors operating from an internal clock, which is derived
from MCLK. The fixed filters set the transmit and re-
ceive gain and frequency response.
The transmit and receive gain can be altered on a per-
channel basis and the per-channel balance impedance
can be selected between two external impedances by
the Am79Q4457 QSLAC-NP device. Control of these
functions is provided by an integrated serial shift regis-
ter and latch per channel. These additional functions
are available on the Am79Q4457 device only.
Data transmitted or received on the PCM highway is an
8-bit, A-law or
µ-law companded code. The QSLAC-NP
device is compatible with both codes. Code selection is
provided via a device pin (A/µ). The 8-bit codes appear
1 byte per time slot. The PCM data is read and written to
the PCM highway in time slots determined by the indi-
vidual Frame Sync signals (FSR
N and FSXN) at rates
from 256 kHz to 4.096 MHz. Both Long- and Short-
Frame Sync modes are available in the QSLAC-NP de-
vice.
Two configurations of the QSLAC-NP device are of-
fered as pictured previously. The Am79Q4457 de-
v i c e wi t h s e ri a l c ont r o l of ga i n a n d b a l anc e
impedance is available in the 44-pin PLCC package
and 44-pin TQFP package. The Am79Q5457 device
without serial control is available in a 32-pin PLCC
package and 44-pin TQFP package.
Serial Control
Package
Part Number
Yes
44 PLCC
Am79Q4457
JC
No
32 PLCC
Am79Q5457
JC
Yes
44 TQFP
Am79Q4457 VC
No
44 TQFP
Am79Q5457 VC