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Patrick De Groote
03/07/07 16:00
Read: 1073 times
Beveren
Belgium


 
#134552 - dte-dce-dce-dte
Responding to: Eugene Yong's previous message
Eugene Yong said:
1. When i was reading a website regarding serial communication and its related signal pins, i came across this quote saying that the TxD pin of the DTE (in this case 8051) is supposed to be connected to TxD pin of the DCE (modem). This is also called as straight through cable. The question here, is why? I thought the TxD of DTE is supposed to be connected to RxD of DCE since the DCE is supposed to accept command from the DTE.


2. Also, how am i supposed to know whether the modem has successfully execute each AT Command i fed into it (before i send additional AT Command)? Is this sufficient just by looking at the TI flag everytime i send out a the last character of a command (Meaning, i am allowed to send new command once the TI flag is asserted)? Or must i wait for a status signal via CTS from the modem?


1) TX pin for a modem is an input pin. TX is always an input for a DCE. it's an output for DTE. For RX the inverse is true. The modem receives data from the line and sends it to the DTE via the RX pin.
That's why you need to mess around with the cable-layout if you want to connect two DTE's back-to-back without DCE's in between.

2. Why don't you try your modem first with a serial port on a PC and hyperterminal (or any other terminal emulation program)?

You will quickly notice that default answer for a correctly sent command is "OK" (most likely followed by CR/LF)
However this need not be. It is possible to configure the modem such that he replies with a digit (cfr return code of a program).

So, why not see for yourself and try it out first...

Oh yes, don't forget that if you are writing your 8052 program, that the modem will echo each character you send to it, unless you disable echo...

regards

Patrick


List of 72 messages in thread
TopicAuthorDate
Serial Communication Related Problem        Eugene Yong      03/06/07 10:49      
   partial answers      Patrick De Groote      03/06/07 11:07      
      Oh yeah, i forgot about that      Eugene Yong      03/06/07 12:09      
   FIRST, THEN, THEN, THEN      Erik Malund      03/06/07 11:10      
      A little bit of sarcasm as usual but often helpful      Eugene Yong      03/06/07 12:25      
         Proper baud rate...      Dave Brooks      03/06/07 12:52      
            baud rate      Erik Malund      03/06/07 13:01      
               calculator      Dave Brooks      03/06/07 13:11      
            modem is autobauding      Jan Waclawek      03/06/07 16:04      
               Noted      Eugene Yong      03/06/07 21:00      
   Some answers      Lynn Reed      03/06/07 11:14      
      Thanks for a patience reply      Eugene Yong      03/06/07 12:33      
   Nothing to add, but ...      Joseph Hebert      03/06/07 11:29      
      i second(ed) that motion      Erik Malund      03/06/07 11:44      
         My location profile?      Eugene Yong      03/06/07 12:38      
            with this known, it would do no good ...      Erik Malund      03/06/07 12:40      
               Radio Shack      Lynn Reed      03/06/07 12:45      
                  Even so      Neil Kurzman      03/06/07 20:44      
                     I can buy it from the local electronic shop      Eugene Yong      03/06/07 20:52      
            Sarcasm      Neil Kurzman      03/06/07 20:52      
               I agree      Eugene Yong      03/06/07 20:57      
      Thanks for understanding and recommendation! - NT      Eugene Yong      03/06/07 12:35      
      More info      Russell Bull      03/06/07 22:28      
         you need to understand the parameters.      Mike Stegmaier      03/07/07 06:28      
            "more valid" evidently means invalid      Erik Malund      03/07/07 07:04      
            not quite      Patrick De Groote      03/07/07 07:29      
               What a wonderful example that when total crap is s      Erik Malund      03/07/07 07:44      
                  lesson      Patrick De Groote      03/07/07 11:43      
            No, it doesn't      Andy Neil      04/03/07 00:37      
   TxD pin to TxD pin?      Eugene Yong      03/07/07 15:31      
      dte-dce-dce-dte      Patrick De Groote      03/07/07 16:00      
         Noted! Thanks!      Eugene Yong      03/07/07 16:20      
            same request question      Jecksons Ben      03/07/07 21:38      
      Meaning of "Transmit"      Andy Neil      04/03/07 04:37      
   same request question 2      Jecksons Ben      03/07/07 21:54      
   Initial command sending code; help me take a look!      Eugene Yong      03/09/07 01:50      
      Make it simple for yourself      Russell Bull      03/09/07 02:50      
         Why the need of circular buffer? Receiving?      Eugene Yong      03/09/07 04:05      
            polling versus interrupt      Patrick De Groote      03/09/07 05:17      
               Check OK string at RXD or DCD at interupt?      Jecksons Ben      03/09/07 21:27      
                  no good      Patrick De Groote      03/10/07 02:14      
                     Voice mode only! No data communication.      Eugene Yong      03/10/07 04:09      
                        you are missing the basics      Patrick De Groote      03/10/07 04:26      
                           NO carrier sent after DCD didn't found      Jecksons Ben      03/11/07 19:54      
                              I do not agree      Patrick De Groote      03/12/07 00:37      
                                 Interupt DCD signal for clear transmission      Jecksons Ben      03/15/07 01:15      
                        For Voice Dialling      Muhammad Fauzan      03/19/07 12:33      
                           and by the way      Muhammad Fauzan      03/19/07 12:36      
                           Sorry for multiposting      Muhammad Fauzan      03/19/07 12:58      
                           The ";" works but...      Eugene Yong      03/22/07 19:46      
                              ";" to return to idle state      Muhammad Fauzan      03/24/07 16:48      
                              +++ with 3 seconds no modem activity      Charles Bannister      03/25/07 03:41      
                                 +++ escape sequence      Andy Neil      03/25/07 07:07      
                                    Monkey See. Monkey Do.      Charles Bannister      03/25/07 08:14      
                                       Now monkey also understand?      Andy Neil      03/26/07 00:26      
                                 Are you mistaken?      Eugene Yong      03/25/07 23:36      
                                    I think so      Andy Neil      03/26/07 00:24      
            Circular buffers      Russell Bull      03/23/07 00:42      
               Initial code for receiving modem response      Eugene Yong      03/26/07 10:38      
                  don't fiddle with the timer, let it run      Erik Malund      03/26/07 10:43      
                     Understood, will run TR1 in global init, thx! - NT      Eugene Yong      03/26/07 10:48      
                  check this out, Eugene...      Dave Brooks      03/26/07 10:52      
                     Ah! Didn't know that! Thanks! -NT      Eugene Yong      03/26/07 11:09      
                     Code; modem commands & responses      Andy Neil      03/26/07 11:23      
   V.250 (formerly V.25-ter) - get it free!      Andy Neil      03/26/07 14:28      
   code,modem command and response      Jecksons Ben      04/01/07 20:20      
   system froze when connected to hyperterminal      Eugene Yong      04/02/07 13:39      
      Your code...      Russell Bull      04/02/07 23:48      
         It should not be a hardware problem since..      Eugene Yong      04/03/07 01:43      
            Not necessarily      Andy Neil      04/03/07 02:42      
      Just taking a stab at it...      Chris Singer      04/03/07 10:22      
         two 'ugly' guesses      Erik Malund      04/03/07 10:44      

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