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MSM6927

1200 bps Single Chip FSK MODEM

Oki Electric Industry 

¡ Semiconductor

MSM6927/6947

Control

Name

LT

CC

RS2

CD1

CD2

RD1

RD2

CDR1

CDR2

SQ

FT

Pin No.

I/O

RS GS-K

Description

Digital loop back test. During digital "High", any data sent on the XD pin will appear

on the RD pin, and any data sent on the RS1 pin will immediately appear on the

4 44 I CS pin. Any data demodulated from the received carrier on the AIN pin will be the

modulated data to implement the transmitted carrier. In this case, sending the

transmitted carrier to the phone line depends on the CC, but never on RS1.

5

2

I

During digital loop back test, the data on this pin becomes a control signal for sending

the transmitted carrier to the phone line in place of RS1.

When an external circuit gives the RS/CS delay time which is not within the device

8 8 I as required, this pin should be connected to the external circuit output.

See Fig. 11-1 or Fig. 11-2 for MSM6927, MSM6947 respectively.

The fast carrier detection output. This pin is internally connected to the input of

the built-in carrier detect delay circuit. When an external delay circuit provides

11 12 O the delay time which is not within the device as required, the CD1 should be

connected to the external circuit input. See Fig. 11-1 or Fig. 11-2 for MSM6927,

MSM6947 respectively.

When an external circuit gives the carrier detect delay time which is not within

the device as required, this pin becomes the input pin for the external circuit

12 13 I/O output signal. In other cases (when using the delay time within the device, the

data on the TS1 (TS) or TS2 is not digital "High"), this pin becomes the Carrier

detect signal output.

The RD1 data is demodulated data from the received carrier and the RD2 is the

13 14 O input of the following logic circuits referred to in Fig. 12-1and Fig. 12-2. for MSM6927

and MSM6947, respectively Usually, the RD1 data is input directly to RD2. In some

14 16

I cases, as input data to RD2, the data that is controlled by NCU (Network control

unit) etc. may be required in stead of the RD1 data.

These two pins are the output (CRD1) and inverting input (CDR2) of the buffer

16 20 O operational amplifier of which the noninverting input is connected to the built-in

voltage reference, stabilized to variations in the supply voltage and temperature.

See Fig. 13. An adequate carrier-detect level can be set by selecting the ratio of

17 21

R8 to R9. Therefore, the loss in the received carrier level by phone-line

I transformer can be compensated by adjusting the ratio of R8 to R9. R8 + R9

should be greater than 50 kW.

When the data rate is 1200 bps and in half duplex mode on two-wire facilities,

22 31

I

the delay function called as receiver-squelch is required. In case of four wire

facilities, this function is not usually required.

When a digital "High" is input to the SQ pin, this function is omitted.

23 32

I

This pin may be used for device tests only. During digital "High", the AO pin will

be connected to receiving filter output instead of transmitting filter output.

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