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CH1788

Surface Mount PLCC 2400bps Modem

Cermetek Microelectronics 

Cermetek Microelectronics, Inc.

CH1788 Surface Mount PLCC 2400bps Modem

Table 2. CH1788 Pin Descriptions (Continued).

PIN NAME TYPE

FUNCTION

8

DTR

I

Data Terminal Ready. Active low. The response to this input is controlled by the

Rn command where n specifies the desired options and includes: returning the

modem to the command state, hanging up the modem, resetting the modem, and

placing the modem in zero power mode.

9

A2

I

Optional Input. Active low. Used when implementing the 911 Priority Pick-Up

circuit or the Line In Use circuit.

10

TXD

I

Transmit Data. Serial transmit data input. Data starts with a high to low transition.

Mark or binary 1 condition is indicated by HIGH.

11

RST

I

Reset. Active HIGH. This input must be asserted HIGH for at least 50 ms to reset

the modem. The RST pin must be returned LOW for normal operation to

commence. If a system reset is not available, let this pin float to enable the internal

reset circuitry.

12

RING

I/O

Ring. Telephone connection requires an active public switched telephone line

(PSTN) for normal operation. This line should be routed to the RJ-11C jack through

the recommended protection circuitry.

13

TIP

I/O

TIP. Telephone connection requires an active public switched telephone line

(PSTN) for normal operation. This line should be routed to the RJ-11C jack through

the recommended protection circuitry.

14

V+

I

Caller ID. Used to connect an external RC network to enable caller ID operation.

See the application circuit in the Schematic 4.

15

V-

I

Caller ID. Used to connect an external RC network to enable caller ID operation.

See the application circuit in the Schematic 4.

18

S1

I/O

Audio Port. Optional audio port input. Allows the internal DAA to be shared with

external voice, tone injection or call progress monitoring applications. See the

application circuits in the Schematic 2 and 3. Note that the CH1788 is FCC

approved for data applications only. Inclusion of voice or other audio functions may

require additional certification by the FCC.

19

S2

I/O

Audio Port. Optional audio port input. Allows the internal DAA to be shared with

external voice, tone injection or call progress monitoring applications. See the

application circuits in the Schematic 2 and 3. Note that the CH1788 is FCC

approved for data applications only. Inclusion of voice or other audio functions may

require additional certification by the FCC.

20

VCC

--

Power Supply. 5 Volt DC +/- 5%. Supply noise should be less than 50 mVpp. Also

available at for 3.3 volt DC operation, upon special request.

21

GND

-

Ground. Circuit ground. Use recommended bypass capacitors between GND and

VCC.

22

RXD

O

Receive Data. Serial receive data output. Data starts with a high to low transition.

Received mark or binary 1 condition is indicated by HIGH.

NOTE: 1. All unused pins should be left unconnected when not required in a specific application,

unless specifically directed otherwise.

2. See DC characteristics before attempting to drive an LED directly from the output of any pin.

2003 Cermetek Microelectronics, Inc.

Page 6

Document No. 607-0018 Revision A2 (07/03)

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