Receiving characters on serial port

**Roaring_Tiger** · 06-08-2004

Hello All,

I am developing a serial port( RS232) application. I have soemproblem in receiving characters. There is communication between two processors.

Receiving a single byte works fine. But if I do not know, how many bytes are there I will have to use following bytes. Since following loop in infinite loop it will never come out. Please let me know..

This is sample routine to read a characters from the serial port.
char lsr, rbr,typeahead[1000];
Int nextput = 0;

PHP Code:


for( ;;)

{

lsr = inbyte ( 0x3FD);



if ( (lsr & 0x01) != 0 )

{

rbr = inbyte(0x3F8);

typeahead[nextput++]  = rbr;

lsr = lsr & FE; // Clear RI bit

}

}

**vsriharsha** · 06-08-2004

Hi,
Let me see if I got you right.

you have a routine to read a single byte from the serial port (let us call it
fnReadSerByte().

Now, you want a way to read all characters that arrive sequentially. Since you dont know how many characters will arrive, you will need a nice loop to do it.

Well, There are two ways to do it.

1. Use the First Byte to represent the number of characters that follow and then use the loop like this.....

Code:

......
int counter;
unsigned char noOfBytes;
......
noOfBytes = fnReadSerByte();
for(counter = 0; counter < noOfBytes; counter++)
  var[counter] = fnReadSerByte();
...
...

2. Use a STOP character (any valid Character that will not be present in your transmission even by mistake), and read the serial port until the received character is NOT THAT CHARACTER.

Hope it Helps.
-Harsha.

**dbtid** · 07-01-2004

I'm not quite sure what you're asking by your example.
First off, are you using interrupts? That's a good way to do it when they're
bursty. You read the Rx register as long as there are bytes to read, then you stop and do
something else (like let the message parser read characters out of the buffer
until IT has a complete message).

**Thantos** · 07-01-2004

Um dbtid the thread is nearly a month old and since the OP hasn't come back to offer more information the thread is dead. Please leave it there.

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