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Rotating bits in a word value

Created by: Sean Greaves at: 12/24/2010 10:46 PM (8 Replies)

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12/24/2010 10:46 PM	Rate (0)
Sean Greaves Experienced Member Joined: 9/27/2006 Last visit: 1/17/2022 Posts: 62 Rating: (0)	Hi I would like to rotate the bits within a word value as below msb 15...........................lsb 0 to lsb 0...............................msb 15 Is a function available in S7 to do this or would a need to create my own function. Thank you and regards Sean

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12/25/2010 1:02 AM	Rate (0)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 10/26/2024 Posts: 6852 Rating: (1365)	I would like to rotate the bits within a word value as below msb 15...........................>lsb 0 to <........................... Is a function available in S7 to do this or would a need to create my own function. Dear member As I undrestood, you just want to swap most sig. bit with least sig. bit in a word(for exampel).I think rotate statements can not do this job.Simply check these code as a simple sample: [code] L MW0 L W#16#7FF7 //FILTER MSB AND LSB AW T MW2 NOP 0 A M0.0 = M3.7 NOP 0 A M1.7 = M2.0 [/code] BR
	Demo Channel on Youtube
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12/25/2010 7:02 AM	Rate (0)
UMENCHO Diamond Member Joined: 3/21/2006 Last visit: 11/1/2024 Posts: 10229 Rating: (1181)	Hello, In cases of communication between CPUs based on different platforms or communication between CPU and HMI for the same reason, you need to use CAW instruction. More info about CAW instruction you could find at Statement List (STL) for S7-300 and S7-400 Programming This issue is caused by method of data storage in a memory in PCs and S7 CPUs. PCs (x86) use so-called low-endian method or byte order. S7 CPUs (MOTOROLA) use big-endian. More on this topic you can learn here. In hdhosseini' example, I think in line 3 should be CAW instead of AW. At the moment I don't have Step7 to test it. But I am sure it will work and you can test it alone. Best regards, Hristo Mihalev

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12/25/2010 10:15 AM	Rate (0)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 11/11/2024 Posts: 3026 Rating: (1057)	Hello Gengus my take on your question is slightly different to the already supplied answers and I believe you want to mirror ALL bits in the word (i.e. swap Bit 0 with 15, swap Bit 1 with 14, swap Bit 2 with 13 etc.). If so I'm afraid to say that there is no ready made block for this in Step 7. You will however find a (SCL programmed) Block called "Reverse" in the OSCAT library (www.oscat.de) which does this for a Byteand could be used asa starting block for your word "bit mirror" block (alternativelywrite your own block). I hope this helps
	Cheers fritz The advice and opinion given in this thread is that of the author and does not necessarily reflect the views of I S Systems Pty Limited. To find out how I S Systems can help you with your automation needs please visit www.issystems.com.au.
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12/25/2010 1:18 PM	Rate (1)
Aret Posts: 2348 Rating: (264)	Well in C it looks like n = ((n >> 1) & 0x5555) \| ((n << 1) & 0xaaaa) ; n = ((n >> 2) & 0x3333) \| ((n << 2) & 0xcccc) ; n = ((n >> 4) & 0x0f0f) \| ((n << 4) & 0x0f0f) ; in STL it would be transformed into (didn't check on PLCSim:^)) L #input PUSH AW W#16#5555 SRW 1 TAK AW W#16#AAAA SLW1 OW PUSH AW W#16#3333 SRW 2 TAK AW W#16#CCCC SLW2 OW PUSH AW W#16#0F0F SRW 4 TAK AW W#16#0F0F SLW4 OW CAW //not sure, but seems if it must be here T #output
Aret Posts: 2348 Rating: (264)
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This contribution was helpful to 1 thankful Users fritz

12/25/2010 7:50 PM	Rate (0)
Sean Greaves Experienced Member Joined: 9/27/2006 Last visit: 1/17/2022 Posts: 62 Rating: (0)	Hi Thank you all for your replies. Merry Christmas Sean

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12/25/2010 8:01 PM	Rate (0)
Sean Greaves Experienced Member Joined: 9/27/2006 Last visit: 1/17/2022 Posts: 62 Rating: (0)	Hi Aret I tried the code you suggested but with my limited knowledge of STL I am getting an "unexpected input end" error on the slw1,swl2 & swl4 commands. Not really sure how to input correctly. Regards Sean

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12/26/2010 3:22 AM	Rate (0)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 11/11/2024 Posts: 3026 Rating: (1057)	Hello Gengus leavea space between the "SLW" and the number and the"unexpected input end" error will be gone. @Aret: Nice work, I did a minor correction to the STL code and ran it through PLCSIM, the logicbelow should do the job: [code]L #input PUSH SRW 1 AW W#16#5555 TAK SLW 1 AW W#16#AAAA OW PUSH SRW 2 AW W#16#3333 TAK SLW 2 AW W#16#CCCC OW PUSH SRW 4 AW W#16#F0F TAK SLW 4 AW W#16#F0F0 OW CAW T #output[/code] I hope this helps
	Last edited by: fritz at: 12/26/2010 1:20 PM Cheers fritz The advice and opinion given in this thread is that of the author and does not necessarily reflect the views of I S Systems Pty Limited. To find out how I S Systems can help you with your automation needs please visit www.issystems.com.au.
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12/27/2010 8:05 PM	Rate (0)
hdhosseini Diamond Expert Joined: 1/28/2009 Last visit: 10/26/2024 Posts: 6852 Rating: (1365)	Dear member This is another solution to make a mirror of a given word.A good example of indirect addressing.Simply is a bitwise swap of bit number 0 to 7 with bit number 15 to 8.Check the attachment for checked result. [code] L #ein T #ein1 L P##ein1 LAR1 LAR2 L P#1.7 +AR2 L 8 llp: T #loop_count A [AR1,P#0.0] = #temp1 A [AR2,P#0.0] = #temp2 A #temp2 = [AR1,P#0.0] A #temp1 = [AR2,P#0.0] L P#0.1 +AR1 L -1 +AR2 L #loop_count LOOP llp L #ein1 T #aus[/code] Best regards hdhosseini Attachment result.JPG (733 Downloads)
	Last edited by: hdhosseini at: 12/27/2010 8:11 PM Demo Channel on Youtube
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