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how to join the low byte nd high byte


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norms

Fri Mar 07 2008, 08:58PM

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im using vb program in reading the data send by my pic16f877 and im getting results alternately.. is it because of the low byt and high byte that is being write in my usart? please help???

CODE:

unsigned int adc_val;

unsigned char low_byte,hi_byte;

void main()

{

USART_Init(9600);

ADCON0 = 0;

ADCON0.ADON = 1;

TRISA = 0xFF;

TRISB = 0;  

PORTB = 0;

while (1)

{

  ADCON0.GO = 1

adc_val = ADC_Read(0);

low_byte = adc_val;

hi_byte = adc_val >> 8;

USART_Write(low_byte);

USART_Write(hi_byte);

low_byte =USART_Read();

high_byte =USART_Read()

if(adc_val==511) //if ADC value read in is 511 

{PORTB = 0xFF;} //display some LED's on PORTB

....

....

.

}

}

for my vb prog:

CODE:

Private Sub CmdExit_Click()

    If MSComm1.PortOpen = True Then

    MSComm1.PortOpen = False

    End If

        End

End Sub

Private Sub Form_Load()

    MSComm1.InputLen = 0

    MSComm1.CommPort = 2

    MSComm1.Settings = "9600,N,8,1"

End Sub

Private Sub Timer1_Timer()

    Dim BytesToRead As Integer

    Dim sData As Variant

    MSComm1.PortOpen = True

    BytesToRead = 1

    Do

        DoEvents

        Loop Until MSComm1.InBufferCount = BytesToRead

        sData= MSComm1.Input

        Text1.Text = (((Asc(sData) * 0.00489)  & " Volts DC"

        MSComm1.PortOpen = False

End Sub

how am i going to read the low and high byte since im only using sData as input

[ Edited Fri Mar 07 2008, 09:50PM ]

Ajay

Fri Mar 07 2008, 09:54PM

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Posts: 3753
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in C you can combine something like this..

CODE:

int combined;

char adcHI, adcLOW;

combined = adcHI;

combined = (combined << 8) | adcLOW;

//now combined is 16-bit value.

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norms

Sat Mar 08 2008, 06:15AM

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Joined: Sat Feb 16 2008, 12:34AM

Posts: 28
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thanks ajay... does this dont mess up with the readings ill be getting in my vb program? ill be using this code as this

unsigned int adc_val;
int combined
char adcHI, adcLOW;;
void main()
{
USART_Init(9600);
ADCON0 = 0;
ADCON0.ADON = 1;
TRISA = 0xFF;
TRISB = 0;
PORTB = 0;

while (1)
{
ADCON0.GO = 1
adc_val = ADC_Read(0);
adcLOW = adc_val;
adcHigh= adc_val >> 8;
combined = adcHI;
combined = (combined <<8) | adcLOW
USART_Write(combined)
combined = USART_Read();

do i need to delete the low_byte and high_byte thing?

[ Edited Sat Mar 08 2008, 06:23AM ]

sashijoseph

Sat Mar 08 2008, 10:00AM

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Joined: Mon Feb 04 2008, 06:26PM

Posts: 554
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Hi.....
First of all you need to understand what you are doing.Let me explain.....
You are reading the adc value and storing it in adc_val which is an int type ie 2-bytes.
When you send data to the PC through the PIC's USART,you can send only 1 byte at a time.Therefore you cannot send adc_val through the USART at once(since it's 2-bytes).So what you do is split the adc_val into two separate bytes ie. hi_byte and low_byte.Now send one byte first(say lo_byte) through USART,then the next(hi_byte).
Now in your VB program you receive these 2 bytes and then recombine them into the original integer adc_val,using the logic depicted above by Ajay(you have to do this in your VB program and not PIC)..

low_byte =USART_Read();
high_byte =USART_Read()

In your PIC program what is this for? Can you explain?

Let there be music........

norms

Sat Mar 08 2008, 10:09PM

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Joined: Sat Feb 16 2008, 12:34AM

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ah ok.thanks... can u give me some info on how i am going to combine this? i've tried but not that succesfull.

Ajay

Sun Mar 09 2008, 07:07AM

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You cannot send variable combine to UART directly, coz its a 16-bit variable and UART is capable of sending 8-bit.

in your first post you are doing right.. i means sending first byte and then second byte. Now you need to do the combining thing in VB.. you can do it something like this

CODE:

Dim Value As Integer = (CInt(FirstByte) << 8) Or SecondByte

 

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norms

Sun Mar 09 2008, 10:06PM

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Joined: Sat Feb 16 2008, 12:34AM

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where i am going to insert the code uve given?
this is my code:

CODE:

Private Sub CmdExit_Click()

    If MSComm1.PortOpen = True Then

    MSComm1.PortOpen = False

    End If

        End

End Sub

Private Sub Form_Load()

    MSComm1.InputLen = 0

    MSComm1.CommPort = 2

    MSComm1.Settings = "9600,N,8,1"

End Sub

Private Sub Timer1_Timer()

    Dim BytesToRead As Integer

    Dim sData as Variant

    MSComm1.PortOpen = True

    BytesToRead = 1

    Do

        DoEvents

        Loop Until MSComm1.InBufferCount = BytesToRead

        sData= MSComm1.Input

        Text1.Text = (((Asc(sData) * 0.00489)  & " Volts DC"

        MSComm1.PortOpen = False

End Sub

[ Edited Mon Mar 10 2008, 05:47AM ]

Ajay

Mon Mar 10 2008, 06:02AM

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i donno much about VB coding and stuff.. only thing i can tell you is.. you need to read two bytes as sent by controller.

Lets say you are sending high byte first and then low byte..
so you need to read them separately one by one.. and store them in two variables and then combine both of them as mentioned above.

e.g.

CODE:

FirstByte= MSComm1.Input

SecondByte = MSComm1.Input

Combined = (CInt(FirstByte) << 8) Or SecondByte

[ Edited Mon Mar 10 2008, 06:03AM ]

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norms

Tue Mar 11 2008, 12:06AM

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Joined: Sat Feb 16 2008, 12:34AM

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Ajay, thank you very much for the help, i've tried using ur code but when im in the Combine = (CInt(FirstByte)<<8) Or Secondbyte the "<<" gives an error, i can only use one <, isn't it a c code "<<"? ... and when i tried checking the value send by the microcontroller the reading was at 255 and changes to 239, is there something wrong with my code?