baudrate 76800

Posted on 2004-04-28
Last Modified: 2010-04-05
I need to interface with an electronic card that works at 76800 baud. I thought it was easy, but I found this speed is not standard. Can I set this speed ???
Question by:gianluca
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LVL 17

Expert Comment

ID: 10937144
Try this

     m_hPort := CreateFile(PChar(sP),
                        GENERIC_READ or GENERIC_WRITE,
                        0, nil,
     if m_hPort = INVALID_HANDLE_VALUE then
// error create
       if GetCommState(m_hPort, dcbPort) then
                 { fill in the fields of the structure }
           dcbPort.BaudRate := 76800;
           dcbPort.ByteSize := 8;  // or ...
           dcbPort.Parity := NOPARITY;
          dcbPort.StopBits := ONESTOPBIT;
         dcbPort.Flags := 0;
            { flag bit fields:
            dcb_Binary, dcb_Parity, dcb_OutxCtsFlow, dcb_fOutxDsrFlow,
            dcb_fOutX, dcb_fInX, dcb_DtrFlow, dcb_RtsFlow
         SetCommState(m_hPort, dcbPort);

Author Comment

ID: 10937227
I try this way :

dcbPort.BaudRate := 76800;

but the actual baudrate sending out from port is 2.2 Kbaud
LVL 17

Expert Comment

ID: 10937348
I remember that long ago the divider for baud rate 38400 was 3.
Achieving 76800 was then impossible.
I've had little hope that maybe something was changed. :(
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Author Comment

ID: 10937507
yes you're right. the divider is 2 for 57600 and 1 for 115200.
But looking at CBR_xx constant, there is also a CBR_128000 and CBR_256000,

how is it possible ???
LVL 17

Expert Comment

ID: 10937552
I've just look at the same. Also CBR_56000.
Maybe try CBR_57600 and then CBR_56000 and watch what is going on?

Author Comment

ID: 10937748
today I can not test what happen when I set speed to CBR_56000, I will do tomorrow in office. Do you have another suggestion ?

PS : I already try CBR_57600 and CBR_115200 and it's OK. I've measured the bitlength using a digital oscilloscope and the timing is correct.
LVL 17

Expert Comment

ID: 10943342
I've tested function
    SetCommState(m_hPort, dcbPort);
from 100 to 256000 with step 100
For baud rates listed below the result is OK for other there is error 87 - invalid parameter and the value of baud rate remains such as last succesfull setting.

100 : OK
Each from this range OK
9600 : OK

10400 : OK

11500 : OK

12700 : OK
12800 : OK

14300 : OK
14400 : OK

16300 : OK
16400 : OK

19100 : OK
19200 : OK

22900 : OK
23000 : OK

28600 : OK
28700 : OK
28800 : OK

38100 : OK
38200 : OK
38300 : OK
38400 : OK

56000 : OK

57100 : OK
57200 : OK
57300 : OK
57400 : OK
57500 : OK
57600 : OK

114100 : OK
114200 : OK
114300 : OK
114400 : OK
114500 : OK
114600 : OK
114700 : OK
114800 : OK
114900 : OK
115000 : OK
115100 : OK
115200 : OK

128000 : 87
256000 : 87

Author Comment

ID: 10943413
How about 76800 ??? is it OK ???

Author Comment

ID: 10943423
You mean others from your list are not OK, right ???
LVL 17

Accepted Solution

mokule earned 125 total points
ID: 10943551
They are not OK.
I'm afraid the only solution is special card something like this

Author Comment

ID: 10943605
Yes I think so. Thanks a lot.

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