Why change the value of int after receiving serial communication?

Question

0.00/5 (No votes)

See more:

In my VC++ code,

A serial sending data to another computer.

It send a structured data like as follows

struct data_format{

char stx; // 0x02
int type;
int seq;
int lenth;
char data[N];
char etx; // 0x03

Once, it send a data to another part;

stx+ type(=0) + seq(=100) + lenth (=220) + data ....

but in the side of receiving data

stx+ stype(=0) + seq(=100) + lenth (=92) + data....

I confirmed every time that the value of lenths are different between sending and receiving part.(220 -> 92)

Is it possible?

What I have tried:

3 more days wasted for this problem

Posted 25-Jun-17 18:14pm

Member 12330615

Updated 25-Jun-17 19:20pm

Add a Solution

Comments

[no name] 26-Jun-17 4:33am

Sounds like you are trying to send binary data in TEXT mode... which can be 7 bits with 1 used as the odd parity bit.

Rick York 27-Jun-17 13:36pm

I recommend using a serial communications analyzer so you can see what is actually going over the line. There are lots of variations of them but they can be very helpful and save a lot of time. You would have known within seconds what your problem was if you had one. If you deal with serial comm very often you really should get one.

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

OriginalGriff · Answer 1 · 2017-06-25T19:20:00

Yes. Look at the values: 92 + 128 == 220. This implies it's a seven bit problem.
The most likely reasons for this are:
1) The communications link between the two devices is set to 7 bits per char (7 bpc), which means that the eighth bit is discarded when it's transmitted.
2) Your software is using a character based value which only holds 7 bits of significant data - it may be that you are using char when you need unsigned char
3) Somewhere in your software you are "masking out" the top bit to prevent negative values.

But without your software, we can't even begin to help you fix.