c++ send hex over uart, leading zero's are dropped on receiving side

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1

Hi,

over the uart port I would like to send out following hexadecimal string C5C301000000000076.
Below there is a snippet of the code I have written but at the receiving end the leading 0’s are dropped.
I receive C5C310000076 instead.
Could anyone give me a hint or a solution?

unsigned char tx_buf[9] = {0xC5,0xC3,0x01,0x00,0x00,0x00,0x00,0x00,0x76}; //unsigned is 0<>255 signed is -128<>127
unsigned char *p_tx_buf = &tx_buf[0]; //points to the first element of the tx_buf

int fd;

//open uart2 for tx/rx, not controlling device
if((fd = open("/dev/ttyO4", O_RDWR | O_NOCTTY | O_NDELAY)) < 0)
printf(“Unable to open uart2 access .\n”);
else
printf(“uart2 opened succesfully.\n”);

if(write(fd,&tx_buf,sizeof(tx_buf))<0)
printf(“ERROR : tx not send.\n”);
else
for(unsigned int i = 0; i < sizeof(tx_buf); ++i)
{
std::cout << std::hex << (int)tx_buf[i];
}
printf(" : tx send \n");

2

I am not sure if I understand--please clarify.

Hi,

over the uart port I would like to send out following hexadecimal string
C5C301000000000076.

...

    unsigned char tx_buf[9] =
{0xC5,0xC3,0x01,0x00,0x00,0x00,0x00,0x00,0x76}; //unsigned is 0<>255 signed
is -128<>127
    unsigned char *p_tx_buf = &tx_buf[0]; //points to the first element of
the tx_buf

   int fd;

    //open uart2 for tx/rx, not controlling device
    if((fd = open("/dev/ttyO4", O_RDWR | O_NOCTTY | O_NDELAY)) < 0)
        printf("Unable to open uart2 access .\n");
    else
        printf("uart2 opened succesfully.\n");

   if(write(fd,&tx_buf,sizeof(tx_buf))<0)

Ok, so you are not sending the hex string, but rather the binary
values. I never ran it this way so I am not sure what might prevent it
from working this way, but the following stack overflow discussion
might be helpful:

            printf("ERROR : tx not send.\n");
        else
            for(unsigned int i = 0; i < sizeof(tx_buf); ++i)
                {
                    std::cout << std::hex << (int)tx_buf[i];
                }
            printf(" : tx send \n");

You do realize that the 'else' block contains just the for() {} loop
and not the printf statement?
(your indentation seems to indicate otherwise) I recommend using
curly braces always even if the conditional block has just one
statement.

3

I only get a case with insert several zero on special platform a few years ago

Finally , I can only use ascII string convert first .then transfer over uart and convert back in receiver

I dont know if this is related with chipset , This case is only happen on QNX platform 6.4.1

4

Could you show us the code on the receiving side?

How many characters do you receive?

Do you convert the receive bytes to strings before printing them?

5

I just saw that your tx buffer is different from your expected string
char tx_buf[9] = {0xC5,0xC3,0x01,0x00,0x00,0x00,0x00,0x00,0x76};

string C5C301000000000076

0x00 doesn’t mean two times 0. If you want to see 18 characters so you need to send 18 characters.