AM79C02AJC datasheet(22/48 Pages) AMD

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Am79C02/03/031(A) Data Sheet

Operating the DSLAC Device

The following describes the operation of either channel

of the DSLAC device. The description is valid for either

Channel 1 or 2. VIN in this data sheet refers to either

VIN1 or VIN2, VOUT refers to either VOUT1 or VOUT2,

and CS refers to either CS1 or CS2.

Power-Up Sequence from VCC = 0 V

The recommended power-up sequence is to apply:

1. Power supply grounds

2. VCC/VEE

3. Signal connections

4. Hardware Reset (02 only)

The software initialization should then include:

1. Select MCLK (Command 6)

2. Software Reset (Command 2)

3. Program filter coefficients and other parameters

4. Activate (Command 5)

Software initialization of the DSLAC device should al-

ways follow any power-up or hardware reset.

Upon initial application of power, a minimum of 1 ms is

needed before CS1 or CS2 may go Low and an MPI

command initiated. If the power supply (VCCD1 or

VCCD2) falls below approximately 2.0 V, the device is

reset and requires complete reprogramming with the

above sequence. Bit 7 of the SLIC Direction Register

reads back as a logical 1 to indicate that a power inter-

ruption has been detected. This bit is cleared when a

software reset command is sent to the DSLAC device.

The RST pin may be tied to +5 V if it is not needed in

the system (Am79C02 only).

Active Mode

Each channel of the DSLAC device can operate in either

the Active (operational) or Inactive (standby) mode. In

the Active mode, the DSLAC device is able to transmit

and receive PCM and analog information. This is the

normal operating mode when a telephone call is in

progress. The Activate command, Microprocessor In-

terface (MPI) Command 5, puts the device into this

state. Bringing the DSLAC device into the Active mode

is possible only through the MPI.

Inactive Mode

The DSLAC device is forced into the Inactive (standby)

mode after a powerup, hardware or software reset, or

is programmed into this mode by the Deactivate com-

mand (Command 1). Power is switched off from all non-

essential circuitry, though the MPI remains active to

receive new commands. The analog output is tied to

ground through an approximate 3 k

Ω resistor. All cir-

cuits, which contain programmed information, retain

their data in the Inactive mode.

Reset State

An active Low, hardware Reset pin (RST) is available

on the Am79C02, which resets the device to the fol-

lowing default state. (For the Am79C02, Am79C03,

and Am79C031, when power is first applied, an internal

power-up reset puts the device into the following de-

fault state.)

1. A-law is selected

2. B, X, R, and Z filters disabled; AISN gain is zero.

3. Digital (GX and GR) gain blocks are disabled,

resulting in unity gain, and analog (AX and AR)

gains are set to unity.

4. SLIC input/output direction is set to the Input mode.

5. Normal conditions are selected (see Command 4).

6. The B-filter Adaptive mode is turned off.

7. Both channels placed in Inactive (standby) mode.

8. Transmit time, receive time, and clock slots are set

to zero.

9. DXA/DRA ports are selected for Channel 1.

10. DXB/DRB ports are selected for Channel 2.

Note: Must be reassigned to DXA/DRA for

Am79C031.

11. MCLK is selected to be 4.096 MHz.

12. Transmit on the negative edge of PCLK. (XE = 0)

13. PCM Delay is inserted.

Reset states 1 to 7 are identical to those of the software

reset (Command 2). The software reset command af-

fects only those channels that have their CS asserted.

Signal Processing

Overview of Digital Filters

Several of the blocks in the signal processing section

are user programmable. These allow the user to opti-

mize the performance of the DSLAC device for the sys-

tem. Figure 8 shows the DSLAC device signal

processing and indicates the programmable blocks.

The advantages of digital filters are:

s High reliability

s No drift with time or temperature

s Unit-to-unit repeatability

s Superior transmission performance

Two-Wire Impedance Matching

Two feedback paths on the DSLAC device modify the

effective two-wire input impedance of the SLIC by pro-

viding programmable feedback from VIN to VOUT. The

Analog Impedance Scaling Network (AISN) is a pro-

grammable analog gain of –0.9375 to +0.935 from VIN

to VOUT. The Z filter is a programmable digital filter, also

connecting VIN to VOUT.

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