AB Serial DF1 CRC Check

Nitay · Dec 8, 2011

Hello Everyone,

I'm trying to communicate with the SLC500 through Serial DF1 and I'm having some difficulties:
1st: I didn't quite get the difference between the Half Duplex and Full Duplex mode - When do i use one and when do i use the other? How do i know which one I'm using? I'm communicating through RS232.

2nd: I'm trying to implement CRC for communication, and I can't figure out what does this algorithm supposed to get me - It seems to converge on 0xFFFF when I have enough bits. I've attached the algorithm I found on the Serial DF1 manual (DF1 Protocol and Command Set Reference Manual)

Any help will be greatly appreciated!

Thank You
Nitay

Mark- · Dec 8, 2011

Hello,

Half and full duplex in DF1 are the same as for plain serial communications. Look up the terms on the web or look in the manual on page 2-2 to 2-4.

As for the CRC, you failed to include the next portion of the page. The validation frame.

Use this frame to validate the CRC
10 02 07 11 41 00 53 B9 00 00 00 00 00 00 00 00 00 00 00 00 10 03 6B 4C

The manual provides a frame with the correct CRC. If your code does not produce the same CRC, you have an error in your code.

Nitay · Dec 8, 2011

Hello Mark, and thanks for your answer,

The CRC, if I understood the document correctly, is supposed to run on the data bytes + the DLE, ETX, right?

Attached are the bytes I'm supposed to run CRC on

Did i get it right?

Thanks
Nitay

Mark- · Dec 8, 2011

Hi,

No.

Per the manual, page 5-3:

The BCC/CRC field contains ...all application layer data bytes between the DLE STX and the DLE ETX

Nitay · Dec 8, 2011

Hello again Mark,

On the algorithm (attached on the first post) it is stated that:
"all link layer data, ETX"
But as you said, on 5-3 they say differently.

Anyway - Just to make sure:

The bytes that should be included in the CRC test should be these:
07 11 41 00 53 B9 00 00 00 00 00 00 00 00 00 00 00 00

And the CRC should be
6B 4C

Is that correct?

Thanks for your help,
Nitay

Mark- · Dec 8, 2011

Hi,

No. They both are the same. You are confusing the link layer frame and the link layer data. The data is between the dle stx and the dle etx. The dle stx and dle etx are the frame, not the data.

>The bytes...

Yes, just the data.

Nitay · Dec 8, 2011

Hi again,

Sorry for the ignorance - But the algorithm states "right" and "left" bits. Is the SLC little-endian or big-endian? When they say "rightmost" bits - Does it mean the lsbit on the LSByte? or the lsbit on the MSByte?

Thanks
Nitay

Mark- · Dec 8, 2011

Hi,

I entered 'right' in the PDF and searched for whole words only and found your answer.

Nitay · Dec 14, 2011

Hello,

I've been all over this document... And implemented as described in it.

I'm getting the right results (Same as several CRC calculators I found on the net) - But they are not the same as the SLCs.

Did anyone manage to do implement the CRC properly? Could you please share the code?

Thank You
Nitay

Mark- · Dec 14, 2011

Hi,

OK, the CRC generator is good. Are you handling the protocol correctly? For example, are you handling a DLE DLE?

Ken Roach · Dec 15, 2011

The part that always got me was in Publication 1770-RM516 on page 5-6, right at the top: "using the value of the link layer data bytes and the ETX byte"

The reference manual has just finished repeating "the data link layer bytes between DLE STX and DLE ETX" several times, and then they drop that little hint in there that you add ETX to the end of the data link layer bytes for the CRC calculation.

07 11 41 00 53 B9 00 00 00 00 00 00 00 00 00 00 00 00 CRC is incorrect, 0xEBED
07 11 41 00 53 B9 00 00 00 00 00 00 00 00 00 00 00 00 03 CRC is correct 0X4C6B

I can't even take credit for noticing this; Lynn Linse (of Digi and Lantronix fame) pointed it out to me.

The CRC generator I use for reference is this one: http://www.lammertbies.nl/comm/info/crc-calculation.html

Nitay · Dec 15, 2011

YES - That was it. I didn't include the ETX on the end.

Tricky one!

Thanks for your help Ken & Mark! And thanks to Lynn Linse!

Mark- · Dec 15, 2011

Hi,

Sorry I missed that.

I am using a lookup table and I looked at the code and it was only using the data bytes (passing just the data bytes to the CRC function). I just went and looked at the CRC code and it adds in the ETX for the CRC calc.

Nitay · Dec 15, 2011

Hello,

That could actually be a good idea!
I'll look into it

Thanks
Nitay

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