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karlelch

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Joined: 30/10/2014
Location: Germany
Posts: 172

Posted: 09:03am 25 Oct 2023

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Hi,

I am trying to send binary data via a COM port. The data contains zeros and it appears that the sending stops if a zero occurs in the data (because a zero does not make sense in a string?).

This is my example code, it sends position commands to a servo controller:

Option Base 0
Option Explicit
Option Escape
Option Default None

SetPin GP5, GP4, COM2
Open "COM2:57600" As #5
Pause 500
Print #5, "\&84\&01\&70\&2E"
Print Lof(#5)

Pause 1000
Close #5

If the second byte (=the servo number) is not zero (e.g., \&01), it works: The respective servo moves; Lof(#5) = 252, indicating that the whole sequence was put into the out buffer.

If the second byte is zero (\&00), the servo does not move and Lof(#5) = 255, suggesting that the sequence was incomplete?

How do you send zero-containing binary data? I am sure, I am missing something.
Any help is appreciated.

Best
Thomas

matherp
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Joined: 11/12/2012
Location: United Kingdom
Posts: 9122

Posted: 09:43am 25 Oct 2023

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Try chr$(0) for the zero character or use bin2str$ to create the string
Edited 2023-10-25 19:47 by matherp

karlelch

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Joined: 30/10/2014
Location: Germany
Posts: 172

Posted: 10:02am 25 Oct 2023

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matherp said Try chr$(0) for the zero character or use bin2str$ to create the string

Wow - that works. Did not expect that to be qualitatively different from \&00, that why I did not think of trying it

Thanks!

pwillard
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Joined: 07/06/2022
Location: United States
Posts: 292

Posted: 12:36pm 26 Oct 2023

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A "0" and a '\00' are very different with regards to the ASCII encoding performed with serial data transfers. For example, the ASCII NUL character '\00' is used to denote the end of the string in C or C++. When a programmer uses a "0" (Ascii character for 0) it is treated as 0x30 in hexadecimal number notation. The decimal equivalent is 48.
Edited 2023-10-26 22:38 by pwillard

karlelch

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Joined: 30/10/2014
Location: Germany
Posts: 172

Posted: 12:58pm 26 Oct 2023

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pwillard said A "0" and a '\00' are very different with regards to the ASCII encoding performed with serial data transfers. For example, the ASCII NUL character '\00' is used to denote the end of the string in C or C++. When a programmer uses a "0" (Ascii character for 0) it is treated as 0x30 in hexadecimal number notation. The decimal equivalent is 48.

Yes, thanks. I see.

In the manual it says "\&hh The byte whose value is given by hh… interpreted as a hexadecimal number". Hence, I expected "\&00" = Chr$(0). And indeed:

> option escape
> ? Hex$(Asc(Chr$(0)), 2), Hex$(Asc("\&00"), 2)
00 00
> ? Asc(Chr$(0)) = Asc("\&00")
1

But in my example (see first post) it was not equivalent.

Best
Thomas

matherp
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Joined: 11/12/2012
Location: United Kingdom
Posts: 9122

Posted: 03:28pm 26 Oct 2023

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The OPs' original code should have worked but it looks like the parser has a bug. I'll look at it for the next RC

karlelch

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Joined: 30/10/2014
Location: Germany
Posts: 172

Posted: 02:56pm 27 Oct 2023

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matherp said The OPs' original code should have worked but it looks like the parser has a bug. I'll look at it for the next RC

Thanks!

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