https://forge.codesys.com/forge/talk/Engineering/thread/a6db2aa3f8/2020-02-27T13:57:04.123000ZRecent posts to Is it possible for a byte to have a negative sign?2020-02-27T13:57:04.123000Z2020-02-27T13:57:04.123000ZdFxhttps://forge.codesys.com/u/dfx/https://forge.codesys.com98e1a426fd8df2e368e2a47dc5478c9d407987b2

<div class="markdown_content"><p>btw, sending a joint angle value coded on a byte seems very low resolution …<br/> Check your doc about wrong type (byte int or dint) as noted by scott</p></div>

2020-02-27T13:57:03.797000Z2020-02-27T13:57:03.797000ZAnonymoushttps://forge.codesys.com/u/*anonymous/https://forge.codesys.com0e58688a406b0d87d140fa1a1b882c5c363272d7

<div class="markdown_content"><p><em>Originally created by:</em> scott_cunningham</p> <p>computers represent numbers as bits. As such, negative numbers do not really exist. Instead, both the sender and the receiver agree to use a bit to signal that the number should be treated as a negative value. It is possible to send a negative value even with the data type as byte. For example, in modbus, dats is sent as WORDS (0..65535). But if both sides agree that WORD 2 should be a negative, then you can send a number from -32768 to 32767. It is even possible to have both sides agree that two WORDS in a row can be a REAL number. </p> <p>So in your problem, it seems to me that your receiver does not expect a negative value. Or as mentioned before, maybe the receiver is expecting 16 bits as a negative. If that is the case, then -1 has to be sent as 0xFFFF (not 0xFF - because 0xFF is actually 0x00FF, a positive number). Check your documentation on the receiver of your data.</p></div>

2020-02-27T13:57:02.982000Z2020-02-27T13:57:02.982000ZCarlos Barríahttps://forge.codesys.com/u/carlos-barria/https://forge.codesys.comc57ab6f2b669c66648ab24dc0ea7d40ee4f8915c

<div class="markdown_content"><p>It is not clear to me. that the value 255 in byte is interpreted as -1 (negative value) in my controller? Use a raspberry as a controlling device</p></div>

2020-02-27T13:57:02.643000Z2020-02-27T13:57:02.643000ZCarlos Barríahttps://forge.codesys.com/u/carlos-barria/https://forge.codesys.combaa73f2c3b6e31b2412995aa566b8d8ce5352f31

<div class="markdown_content"><blockquote> <p><strong>I-Campbell hat geschrieben:</strong><br/> Sending byte value 255 is correct if you want to send -1.<br/> What is your receiving device? Your receiving device needs to interpret 0xFF as -1.<br/> Is it even expecting an 8 bit value? If it's expecting more, you might need 0xFF.<br/> The best we to display the same bits as different interpretations is with a DUT UNION.</p> </blockquote></div>

2020-02-27T13:57:02.275000Z2020-02-27T13:57:02.275000Zi-campbellhttps://forge.codesys.com/u/i-campbell/https://forge.codesys.combcfaf780aaaf98c68dda1711c0a09930cca09987

<div class="markdown_content"><p>Sending byte value 255 is correct if you want to send -1.<br/> What is your receiving device? Your receiving device needs to interpret 0xFF as -1.<br/> Is it even expecting an 8 bit value? If it's expecting more, you might need 0xFF.<br/> The best we to display the same bits as different interpretations is with a DUT UNION.</p></div>

2020-02-27T13:57:02.011000Z2020-02-27T13:57:02.011000ZCarlos Barríahttps://forge.codesys.com/u/carlos-barria/https://forge.codesys.com78e09483c48c43e554b89bd3db899d9f4eca9f4f

<div class="markdown_content"><blockquote> <p><strong>dFx hat geschrieben:</strong><br/> sign is just an interpretation of the binary data. Usually, the sign is the most significant bit in your data.<br/> in your case, using a byte, means 8 bits of data. Max unsigned range is 0~255. But if you interpret it as signed then range is -128~127.<br/> so it is just a different method in evaluating the value that causes your problem.<br/> so your solution may be in correcting how you evaluate it.<br/> Why do you need to send some negative values ?</p> </blockquote> <p>I need to send messages that contain joint angle values, therefore it is necessary to send some negative angles. I have tried changing the variable to SINT, but it does not recognize the sign.</p></div>

2020-02-27T13:57:01.794000Z2020-02-27T13:57:01.794000ZdFxhttps://forge.codesys.com/u/dfx/https://forge.codesys.com546bfecb006e21326cbffc1cdc1ea3ee4b6819a9

<div class="markdown_content"><p>sign is just an interpretation of the binary data. Usually, the sign is the most significant bit in your data.<br/> in your case, using a byte, means 8 bits of data. Max unsigned range is 0~255. But if you interpret it as signed then range is -128~127.</p> <p>so it is just a different method in evaluating the value that causes your problem.</p> <p>so your solution may be in correcting how you evaluate it.</p> <p>Why do you need to send some negative values ?</p></div>

2020-02-27T13:57:01.053000Z2020-02-27T13:57:01.053000ZCarlos Barríahttps://forge.codesys.com/u/carlos-barria/https://forge.codesys.com63ddd25ff8506c831a4c552a31d36a8e8af95397

<div class="markdown_content"><p>I am working with the CAN API library and I need to send negative data but the negative data converts them to positive. How can I send negative bytes?. <br/> For example I send a byte -1 and the program converts it to 255</p></div>