Serial Communication : 8bit

dkwon

Hello,

I am doing serial communcation between pc and javelin.
Since using sendByte funtion, I can only send 8bit data. Is there any way to get higher resolution data?

Thanks in advance.

Peter Verkaik

You can send an int (16bits) by sending the lowbyte, then the highbyte.

int c;

txUart.sendByte(c);

txUart.sendByte(c>>>8); //notice the unsigned shift

On the receiving side (eg. pc), the program must·know when to expect an integer.

You could send a synchronize value that is never an existing value, for example 0xFFFF.

regards peter

dkwon

I still have a problem.

How can i send negative value?

In PC side java, how can i convert the data from javelin?

Peter Verkaik

Negative values are send in the same way.

A signed integer of 16bits has dedicated b15 as the sign bit.

On the receive end:

int L = receiveByte(); //assuming you send low byte first

int H = receiveByte();

int value = (H<<8)|(L&0xFF); //16bits value

regards peter

dkwon

It is beautiful. I finally succeeded it. However, I still have a problem with negative value.

Can you give me an example of negative values also for Javelin side and PC side?

How can I know it is negative in PC side?
Do I have to send additional byte to notify it is negative like 0:negative and 1: positive?

For synchronization, you mention that I can use 0xFFFF. But javelin complains the number is out of something.
Please give me how can I synchronize PC and javelin.

Thanks alot!!

Peter Verkaik

Integers in the javelin are always 16bits signed.

For unsigned 16bits values use short.

Example:

int p = -32768;

short q = 0x8000;

int r = (short)0x8000;

p,q and r all have the same value, namely 0x8000,
but p and r are treated as signed.

positive values 0 to 32767 (hex 0x0000-0x7FFF)
negative values -32768 to -1 (hex 0x8000 to 0xFFFF)

if -32768 is never a valid value for your·data, you can use 0x8000 to synchronize.


On the receive end (your pc program), ints may be 32bits.
In that case assembling a 16bits value always is positive.

Then you can do this:
int L = receiveByte(); //lowbyte
int H = receiveByte(); //highbyte
int R = (H<<8)|(L&0xFF); //16bits value
int result = (R >= 0x8000) ? R-65536 : R; //make negative int

If your pc program has a 16bits integer type (like int16) you could use that.

regards peter


Post Edited (Peter Verkaik) : 10/26/2005 5:01:05 PM GMT

dkwon

Thanks alot peter!