73M223

1200 Baud FSK Modem

5

APPLICATION INFORMATION

The

73M223

modem

chip

allows

low

cost

communications

in

a

private

network,

utilizing

twisted pair telephone wires. This chip is the prime

choice of those designers who require an efficient,

high performance modem solution for dedicated

private networks, HDX dial-up and other specialized

applications.

Such

applications

include

credit

verification systems, point-of-sale terminals, remote

process control, satellite and RF telemetery, private

data

links

and

acoustic

modem

designs.

No

microprocessors

or

external

adjustments

are

necessary with this device.

Utilizing a crystal input of 3.1872 MHz*, the 73M223

is a V.23 main channel 1200 Baud, FSK modem.

The signaling frequencies generated are 1302 Hz for

a logic “1” and 2097 Hz for a logic “0.” Crystals with

frequencies varying between 330 kHz to 7.0 MHz or

higher can be used. The baud rate and signaling

frequencies vary linearly with variation in crystal

frequency. If compatibility with V.23 is not required, a

color burst 3.579 MHz crystal can be used as long

as the other modem uses the same frequency offset.

A typical implementation on the 73M223 is shown in

the figure below. A 73M1550 UART receives data to

be transmitted from a microprocessor bus. The

UART sends the data in a serial format to the

73M223 modem after inserting the necessary start

and stop bits. The modem transmits this data to the

far end via the TXA pin. Full-duplex operation can be

implemented by utilizing separate transmit and

receive circuits. A USART can be used instead of a

UART if synchronous operation is desired. With

synchronous operation, a USART uses the modem’s

SYNC signal for timing to sample the received data,

and the modem’s CLK signal for timing to send data

to be transmitted.

* Available from Ecliptek Corp. (714) 433-1200 and

SMI Inc. (916) 477-5085.

73M223 TYPICAL APPLICATION

RXA

TXA

R2

100K

C5

VDD

0.1 µF

R3

100K

0.1 µF

C3

1 µF

C4

VDD

C2

30 pF

Typ.

3.1872

MHz

Y1

R1

1 M

Ω

C1

30 pF

Typ.

U1

1

2

3

4

5

6

7

8

VDD

RXA

CAP

RXF

TXA

CLK

OSC2

OSC1

TXD

FIL

TEST

RXD

7;

VSS

6<1

SYNC

73M223

9

10

11

12

13

14

15

16

U1

28

27

26

25

24

23

22

21

20

19

18

17

16

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

VCC

'&'

'65

&76

MR

'75

576

A0

A1

A2

INTRPT

5,

5'

VSS

:5

XOUT

XIN

&6#

SOUT

SIN

D7

D6

D5

D4

D3

D2

D1

D0

H

O

S

T

I

N

T

E

R

F

A

C

E

16C550