¡ Semiconductor

MSM6926/6946

6/25

Input/Output

Name

Pin No.

RS GS-K

I/O

Description

CS

63

O

Clear to send signal output. The digital "High" level indicates the "OFF" state and

digital "Low" indicates the "ON" state. This output goes "Low" at the end of a delay

(RS/CS delay) initiated when RS1 (Request to send) goes "Low".

Request to send signal input. The digital "High" level indicates the "OFF" state.

The digital "Low" level indicates the "ON" state and instructs the modem to enter

the transmit mode. This input must remain "Low" for the duration of data

transmission. "High" turns the transmitter off.

RS1

74I

transmitted as "Mark". Digital "Low" will be transmitted as "Space". No signal

XD

99I

"High" indicates "Mark" and digital "Low" indicates "Space". For example, under

the following condition, this output is forced to be "Mark" state because the data

may be invalid.

• When CD2 (Carrier detect) is in the "OFF" state.

RD

10

10

O

The SG1 and ST2 are built-in analog signal grounds. SG2 is used only for

Carrier detect function. The DC voltage of SG1 is approximately 6 V, so the

analog line interface must be implemented by AC coupling. See Fig. 9. To make

impedance lower and ensure the device performance, it is necessary to put

bypass capacitors on SG1 and SG2 in close physical proximity to the device.

SG2

18

22

O

SG1

20

24

O

This is the input for the analog signal from the phone line. The modem extracts

the information in this modulated carrier and converts it into a serial data stream

for presentation at RD output.

21

26

I

This analog output is the modulated carrier to be conditioned and sent over the

phone line.

25

34

O