OCM-22 Datasheet(数据表) 3 Page

3 page

Agere Systems Inc.

Product Brief Rev 1.0

April 2005

One-Chip Modem for Embedded Applications

OCM-22

Functional Description (continued)

Figure 3. Parallel Interface to DIA Port

5-8104 (F) a

OCM-22 DEVICE

HD[7:0]

HA[1:0]

HRDN

HWRN

HINTR

HCSN

DATA[7:0]

ADDR[1:0]

READN

WRITEN

INTRPT

ADDRESS

DECODE

Internal PLL for Low-Speed Crystal Support

OCM-22 supports low-speed, external crystals by

incorporating a PLL to support lower-cost crystals and

to ease the effort of minimizing EMI. If future code

needs higher clock rates, an internal multiplier can pro-

vide this without recertification or redesign of the exter-

nal hardware. OCM-22 requires an external 29.4912

MHz crystal or oscillator.

PWM Speaker Interface

The speaker driver employs a pulse-width modulated

algorithm, where 8-bit two's complement data is modu-

lated by a triangle wave. The following diagram shows

the recommended speaker configuration. This inex-

pensive configuration drives a low-impedance speaker

while obtaining a suitable volume. The SPKR signal is

fed to a transistor through a low-pass filter to remove

the carrier signal (cut-off frequency = 4 kHz).

Power Requirements

Both the OCM-22 device and the CSP1034C are

manufactured in low-power CMOS technology and are

designed to operate using only a single 3.3 V supply.

During operation, OCM-22's on-chip PLL can be set to

provide only the minimum internal clock rate required.

The CSP1035A is also manufactured in low-power

CMOS technology. However, the CSP1035A is fully

line powered. A shunt regulator maintains a monitored

2.7 V supply, during off-hook conditions. If the voltage

falls below 2.2 V, the chip saves its registers and goes

into reset. This allows the CSP1035A to retain the reg-

ister settings during a call bridge where the tip/ring volt-

age can collapse to 0 V for up to 400 ms and start up

again at the completion of the call break.

Figure 4. Lower-Impedance Speaker Configuration

5-8105 (F)

SPKR

3.3 k

Ω

10 k

Ω

6800 pF

+3.3 V

AT-08

FDV301N

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