CH1787 데이터 시트보기 (PDF) - Cermetek Microelectronics

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CH1787

Small Footprint Hardware Controllable 2400bps Modem

Cermetek Microelectronics 

Cermetek Microelectronics, Inc.

CH1787 Small Footprint Hardware Controllable 2400bps Modem

Figure 4. CH1787 Application Diagram of Test Circuit.

PIN NAME I/O

1 RING I/O

2 TIP I/O

7 RXA O

8 DTR I

9 ANS I

10 V/D O

11 RST1 I

12 RI

O

Table 1. CH1787 Pin Descriptions.

FUNCTION

RING. Directly connects to the telephone line’s RING lead through a user’s supplied RJ-11C

jack.

TIP. Directly connects to the telephone line’s TIP lead through a user’s supplied RJ-11C jack.

ANALOG VOICE INJECT. Transit and receive analog voice signal. Let float if not used.

DATA TERMINAL READY input. Active LOW. Switching off a DTR can either return modem

to command state, disconnect phone call, or reset modem. DTR should be set LOW when not

used.

ANS. Used to manually answer an incoming call. Input has two modes of operation

depending on its state during reset. When ANS is low during reset, the CH1787 will go off

hook in the answer mode and send an answer tone continuously waiting for an originating

tone. This mode of operation is used on a dedicated non dial-up telephone line (leased line).

When ANS is high during reset, the modem will initiate an answer tone whenever the ANS Pin

goes low during normal operation. The modem will send the answer tone for 30 seconds and

then stop. The CH1787 will then repeat the answer tone sequence as long as ANS is low.

VOICE/DATA. Used to switch between telephone and modem line use. When low, the

modem is in the control mode and a voice circuit can be switched out, RXA, TXA when high

the modem is in the data mode and the input should be TXD/TXD.

RESET (active high). Must be asserted HIGH for at least 10ms to reset the modem. RESET is

then returned LOW for normal operation. If no system reset is available, let this pin float to

enable internal reset.

RING INDICATION. This signal follows the frequency of the ringing signal which is typically 20

to 40 Hz for 2 seconds on and 4 seconds off.

2002 Cermetek Microelectronics, Inc.

Page 4

Document No. 607-0002 Revision B (03/02)

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