General Tips and Techniques


The following tips and techniques can help the exchange of information between the software controller and the modem command processor.

Commands in the command line should be ordered starting with the safest and ending with the most risky. Risk is defined as the potential to generate an ERROR result code, causing the remainder of the command line to be ignored.

Any command that may return an ERROR result code should be anticipated. This or other unexpected results can be ignored unless the command is critical (configuration or call placement).

Send I0 - Display Product Code or I4 at 1200 bits/s, which is supported by the majority of modem products. A modem reset (&F or Z) should be performed at 1200 bits/s before sending the identification commands.

Setup processing can be speeded by sending all but the last D - Dial Command or S0 - Ring After Which To Answer command at the highest DTE rate supported by the modem. The last command must be sent at the speed at which the connection should be made (except Vseries products which specify this with S37).

Any dependency on proper cabling can be eliminated by avoiding techniques that depend on RS-232 signals.

Have the software scan for result codes, rather than depending on the condition of the CD line.

Transparent flow control should be used with Vseries products rather than with RTS/CTS signals.

The Hayes Patented Escape Sequence with guard time process and Hn - Control The Switchhook command should hangup instead of terminate a connection by dropping DTR.

Any unexpected RING result codes may indicate the last command may not have been processed correctly. The command should be-issued.

The following is a sample Controller/Modem Exchange referenced to a clock. 
Clock    Controller             Speed           Modem                             

(1.2 kbits/s)                                     

00000    ATZ<CR>                                                             

00034                                           ATZ><CR>                      

00068                                           (1 s to do reset)                 

01068                                           0<CR>(V0 stored as default)  

01084    (delay additional 600                                                    


         ms)                                                                       

01684                                                                             

         ATEQV1S0=0S12=10S4=3H1<CR>                                                                         

01884                                           ATEQV1S0=0S12=10S4=3HI&ltCR>   

                                                (echo)                             

02084                                                                             

                                                <CR><LF>960<CR><LF>

02142                                           <CR><LF>OK<CR><LF>

                                (19.2 kbits/s)                                    

02192                                                                             

         ATM0X4L1S12=10S2=1&Q5W1S36=7S37=9&K5&ltCR>                                                 

02206                                           <CR><LF>OK<CR><LF>

02209                                                                             

         ATDT9W14045551212<CR>                                                 

38000                                           <CR><LF>CARRIER           

                                                2400<CR><LF>              

45000                                           <CR><LF>PROTOCOL:         

                                                NONE<CR><LF>              

45010                                           <CR><LF>CONNECT           

                                                2400<CR><LF>              

                                (2.4 kbits/s)                                     

(Connection Established)                                                               

                                (2.4 kbits/s)                                     

00000    (delay 300 ms, need                                                      

         200, add 100 for safety)                                                  

00300    (escape char is ^A,                                                      

         S2=1)                                                                     

00313                                           (waits 200 ms)                    

00513                                           <CR><LF>OK<CR><LF>

00538    ATHE1S2=43S12=50W0&Q0<CR>                                                 

00630                                           <CR><LF>OK<CR><LF>
Where to Go from Here
With the information provided here, you should be able to configure a modem with AT commands for a variety of communication environments. If you are just starting out with communications programming, this information should provide you with sufficient tips to use the modem features through a software program of your own.

If you are, or would like to become, a registered Hayes Software Developer, you may receive additional technical material on Hayes products. For information on qualification and registration procedures, contact Hayes Customer Service at the telephone number and/or address provided with your modem package.


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