AM79Q02JC datasheet(36/68 Pages) ETC1

36 / 68 page

Am79Q02/021/031 Data Sheet

Figure 13. Robbed-Bit Frame

Default Filter Coefficients

The QSLAC device contains an internal set of default

coefficients for the programmable filters. These coeffi-

cients were determined to allow reasonable system

performance for initial power-up non-programmed situ-

ations, such as may exist before a system processor

has opportunity to program any coefficients.

The default filter coefficients are calculated assuming

an Am7920 SLIC with 50

Ω protection resistors, a

178 k

Ω transversal impedance (ZT), and a 90.5 kΩ re-

ceive impedance (ZRX). This SLIC has a transmit gain

of 0.5 (GTX) and a current gain of 500 (K1). The trans-

mit relative level is set to +0.28 dBr, and the receive rel-

ative level is set to –4.39 dBr. The equalization filters (X

and R) are not optimized. The balance filter was de-

signed to give acceptable balance into a variety of im-

pedances. The nominal input impedance was set to

815

Ω. If the SLIC circuit differs significantly from this

design, the default filters cannot be used and must be

replaced by programmed coefficients.

To obtain this above-system response, the default filter

coefficients are set to produce these values:

GX gain = +6 dB, GR gain = –8.984 dB

AX gain = 0 dB, AR gain = 0 dB

R filter: H(z) = 1, X filter: H(z) = 1

Z filter: H(z) = 0, B filter H(z) = 0

AISN = cutoff

Notice that these default coefficient values are retained

in a read-only memory area within the QSLAC device,

and those values cannot be read back using any data

commands. When the device is selected to use default

coefficients, it obtains those values directly from the

read-only memory area, where the coefficient read

operations access the programmable random access

data memory only. If an attempt is made to read back

any filter values without those values first being written

with known programmed data, the values read back

are totally random and do not represent the default or

any other values.

COMMAND DESCRIPTION AND FORMATS

Microprocessor Interface Description

A microprocessor can program and control the QSLAC

device using the MPI. Data programmed previously

can be read out for verification.

Commands assign values to the following channel

parameters:

Transmit time slot

Receive time slot

Transmit clock slot

Receive clock slot

Transmit gain

Receive loss

B-filter coefficients

X-filter coefficients

R-filter coefficients

Z-filter coefficients

AISN coefficient

Read/Write SLIC Input/Output

SLIC Input/Output Direction

Select A-law, µ-law, or linear code

Select Transmit PCM Port A or B or both

Select Receive PCM Port A or B

Programmed/Default B filter

Programmed/Default Z filter

Programmed/Default X filter

Programmed/Default R filter

Programmed/Default GX filter

Programmed/Default GR filter

Enable/disable AX amplifier

Enable/disable AR amplifier

Select test states

Select Active or Inactive (standby) state

Commands are provided to read values from the

following channel monitors:

SLIC status

Transmit PCM data

PCLK

Normal Frame (Not Robbed-Bit)

PCLK

Robbed-Bit Frame

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