Re: [avr-chat] how can connect two avr with standard telephone line

[Hugo González Monteverde]

> i need transfer data with standard analog telephone line 
> some one sugesst use avr(ATMEGA16) with external modem
> some one segesst use avr with MT8888 dtmf tansmiter/resiver

DTMF would be if you have to send little information, if data amount is 
significant, use a modem.

> ineed transfer serial data (19200 bit per second) in half duplex mode with
> this system
> isend ATcommad to modem with AVR and modem do not work 

Hi,

I don't know whare you're at, so I must ask many things:

I suppose you're connecting your AVR to a serial modem, then to a 
dial-up phone line, then to a modem, then to a PC or another AVR.

AVR--MAX232---MODEM----TELEPHONE LINE----MODEM---MAX232 --AVR


Do you have a level converter such as the MAX232 or similar before the 
modem?

What flow control does the modem expect? Normally you wont use any flow 
control with a simple system (too many pins, and level conversion). Have 
the modem see crossed control lines: RTS/CTS and DSR/DTR (specially this 
last one) Modem handshaking is sometimes not that easy.  Google for 
"null modem"

What is the data rate to the modem?? it need not be the same you're 
using *between* the modems. Check the modem manual for that, or try 
57600 or 115200 (they're made for fast UARTS in PC's)

I suggest you connect the serial port in the AVR to a PC FIRST and make 
sure the PC can see what you're sending and viceversa (simple echo 
program will do). Then check the settings you use from the PC to get a 
response from the modem and copy that to the AVR.

HTH

Hugo