Instrument Control (GPIB, Serial, VISA, IVI)
Receive incorrect information through serial
How do you know that you start reading at the beginning of a 10 byte piece.
Maybe you start reading somewhere half way and I don't see something that can capture a new start.
Also send the vi instead of (both vi's in fact) and you seem to initialize the port before each read that anyhow causes trouble.
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As a first step, you should post your code in the LabVIEW forum, because it is highly flawed.
- No, a greedy polling loop is never appropriate!
- If you want array elements in order, there is no need to wire indices of index array.
- There is no way to tell how your two disconnected code fragments relate to each other?
- Yes, frame shifts are a possibility and you need to handle them.
- Your "x+y" local variable should be replaced by a shift register.
- What's in the other cases of the case structure?
- What do the subVIs do?
- ...
Hi there
I'm writing a program for serial communication. The information of FPGA is sent to a computer through a USB using CH340 serial converter. Data is being read through LabVIEW software using the VISA Configure Serial Port VI and VISA Read modules. The submitted information is 8-bit and is sent in a 10-byte package. However, when it is read, the sent bytes are disordered.
In the image below, you can see the part of the FPGA code that is for sending information. This code reads and sends a memory 1024 times.
First two bytes of constant, then two bytes of data and one byte of constant, then two bytes of data and another byte of constant and two bytes of data are sent.
In the image below, you can also see the part of the code that receives the information in LabView.
After reading the information, 10 bytes are separated and we check the place of the constants by a condition that is correct, and if it is correct, the data will be sent to the next stage for processing.
I really appreciate if you could help me to solve this problem
- You are waiting for a button to be pressed. There is no need for sub-nanosecond resolution, spinning the loop as fast as the computer allows, using 100% CPU doing nothing but polling one button (See also). If you would place a 50ms wait inside that loop, the CPU use would be millions of times less keeping your computer cool and saving electricity/battery. Of course the really correct way is to have a state machine architecture. Your sequence frame has probably no purpose and can be deleted.
- You don't need to wire the indices! You get the same 10 elements! Less diagram clutter. Fewer places for bugs to hide, e.g. if you accidentally type one number wrong.
- Exactly. There is no visible relation between your two pictures. We like to see the entire code, so attach your VIs!
- if the other end is continuously sending ...012345678901234567890123456789012... there is no guarantee that a 10 element segment is 0123456789, could equally be 4567890123. That's a frame shift.
- Well, learn about shift registers and feedback nodes. There is no reason to use front panel elements (x+y indicator in this case) to store data between iterations. Data belong on the diagram unless it is for user interaction.
- Your code shows the presence of subVIs. Since we don't have these, we cannot debug.
In summary. Do a few basic LabVIEW tutorials first. Attach your code (VIs, not pictures!) and make sure that all controls have typical default values.
@altenbach wrote:
if the other end is continuously sending ...012345678901234567890123456789012... there is no guarantee that a 10 element segment is 0123456789, could equally be 4567890123. That's a frame shift.
To elaborate on this a little bit...You need to define a message format to that the receiver knows when the message begins and ends. It looks like this is a binary message that you are currently sending. Therefore, I would do something like have a start byte, typically 0x2 (Start Of Text byte as defined by ASCII), followed by your 10 bytes of data, and finally a checksum of some sort. The checksum could be something as simple as a sum of all the data bytes. So I am basically recommending adding 2 bytes to your message. This is also with the assumption that all of the messages are 10 bytes of data. If that changes, then you will need something to tell the receiver how many bytes of data are in the message.
So with this setup, you will first need to make sure the Termination Character is turned OFF. It is an input on the top of the VISA Configure Serial Port (defaults to TRUE). Then I would read a single byte until 0x2 is read. Once that byte is read, read 11 bytes (10 data bytes plus the checksum), perform the checksum operation and verify it is correct. If correct, you know you have a good message and can do whatever with it. If the checksum fails, throw away the data. Regardless, go back to reading 1 byte at a time until 0x2 is read.
If you want even more details, go watch this: VIWeek 2020/Proper way to communicate over serial
Around half way, I get into the binary protocols.
