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MODEM - LINE CONNECTED

HARDWARE

COM24 modem

COM24 modem


Serial Port 2 can conveniently be connected to a modem that accepts 'AT' commands. COM24 is a miniature type well matched to TDS2020F that takes little current. It can be switched off to save power when not in use, and is small, only 61 x 57 x 25mm in size including the 25-pin D-socket. The modem is capable of 2400 baud and 1200 baud; the baud rate is selected automatically from the first incoming signal from the TDS2020F. To avoid shared line disruption the modem (from version 3) prior to making a call will 'listen' on a shared line for voice or data transmission and will not seize the line if it is in use. The temperature specification is -30C to +70C.

 

The power supply needed is +6 to 16V. Typical current consumption is

 

Active

30mA (max. 40mA)

Idle

4ma (max 6mA)

Power-down

3A (max. 10A)

 

TDS2020F

Pin

Modem 25-pin socket

Function

Connections for modem model COM24:

 

 

 

SOUT2

c13

2

Data transmit

SIN2

c14

3

Data receive

GND

c32

7

Ground

VIN

a32 (+6 to 12V)

15

Modem power supply

Connections for most PC modems:

 

 

 

SOUT2

c13

2

Data transmit

SIN2

c14

3

Data receive

GND

c32

7

Ground

VIN

a32 (+6 to 16V)

4

Request to Send

VIN

a32 (+6 to 16V)

20

Data Terminal Ready

 

The COM24 has an internal voltage regulator with input on pin 15 and output on pin 14. To drive the unit from the TDS2020F's switched +5V output, connect pin c15 to both pins 14 & 15 on the COM24.

The telephone connection is by a 6-way socket. A UK telephone lead is supplied unless otherwise agreed.

MAKING A CALL

A TDS2020F can make or receive a call, file #MODEM.TDS is for the former. Use 1200 2BAUD or similar to initialise Port 2. Then, in order, use these words:

 

?MODEM

Establish that a modem is attached and responding.

DIAL

Call a telephone number fed as a parameter in string format.

HANG

Replace the 'receiver' on hook.

 

Between the second and third operations serial Port 2 can exchange data with the remote computer. To test operation of your system use library file #TIMEEUR.TDS or #TIMEUSA.TDS to automatically dial up a national time service, collect the current date and time, set the TDS2020F clock accurately then hang up-all automatically.

RECEIVING A CALL

If the TDS2020F is to receive a call no software apart from the #SERIAL2.TDS Port 2 driver is needed. Make the connections above and use *KEY? to let your software know when something is arriving on Port 2 from the modem.

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