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S5 DO Instruction

Created by: Ohhh Whats Occuring! at: 12/6/2011 1:24 PM (7 Replies)

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12/6/2011 1:24 PM	Rate (0)
Ohhh Whats Occuring! Posts: 13 Rating: (0)	hi, been looking at a bit of exisiting code in one of our systems for a while and ill still non the wiser to what its doing, was hoping someone could shed some light on this for me. im familiar with indirection and a little with the S5 DO instruction but i still cant quite work out what this is doing. C DB105 DO DW 11 T DW 11 L DW 11 L KF +1 +F T DW 11 is it just incrementing the counter in DW 11 to the next address? thanks for you help.
Ohhh Whats Occuring! Posts: 13 Rating: (0)
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12/6/2011 2:12 PM	Rate (0)
LXG Posts: 33 Rating: (0)	HI, It is about index addresing. I'm missing a instruction before C DB105. Should be a value assigned to the DW 11. Here is example how "DO" instruction works. LKF +120 Load value 120 in to acc1 T FW 14 Transfer 120 to the FW14 DO FW 14 Load contains of the FW 14 L IB 0 Raed or load IB 120 Hope this will help
LXG Posts: 33 Rating: (0)
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12/6/2011 2:54 PM	Rate (0)
Ohhh Whats Occuring! Posts: 13 Rating: (0)	thanks for the reply LXG. the code is part of a much much bigger block with tons of jumps all over and not very well commented so im struggling a little with finding what bits are what. The bit im struggling with is the instructions after the DO. i thought that you needed to refereance DW/F 0 like in your example. ... DO FW1 L FW 0 so it loads whatever is the pointer in FW1...but there is no instruction with a zero. what am i missing? (feel really quite thick now, i thought i was getting the hang of S5 :). thanks
Ohhh Whats Occuring! Posts: 13 Rating: (0)
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12/6/2011 3:21 PM	Rate (0)
LXG Posts: 33 Rating: (0)	Hi, Maybe is not resetting to zero, maybe is just copying values? I'm just guessing... Yes you're right. It's load whatever is contains of FW1. So you should follow the progarmm lines very carefuly to understand what is program doing. Good luck
LXG Posts: 33 Rating: (0)
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12/6/2011 5:04 PM	Rate (0)
BeVee Gold Member Joined: 7/18/2011 Last visit: 10/9/2023 Posts: 521 Rating: (91)	Hi Oh Whats Occuring The next operation of a DO instruction is combined through logic OR with the parameter specified in the data word and executed. I’ll give 2 examples: L KF +5 T DW 11 DO DW 11 T DW 11 //Executes instruction T DW 15 L KF +1 T DW 11 DO DW 11 T DW 11 //Executes instruction T DW 11 L DW 11 //This parts increments DW 11 by 1 L KF +1 +F T DW 11 Kind regards BV

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12/6/2011 5:42 PM	Rate (0)
Ohhh Whats Occuring! Posts: 13 Rating: (0)	ahhh that makes much more sense. thank you BeVee
Ohhh Whats Occuring! Posts: 13 Rating: (0)
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12/8/2011 11:45 AM	Rate (0)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 10/4/2024 Posts: 3024 Rating: (1054)	Hello Ohhh Whats Occuring! I'm going out on a limb here as I can't test it right now, but my understanding of the DO instruction differs from BeVee's advise. Put simple, as far as I'm concerned it does NOT matter what number you put into the instruction that follows a DO command, as it will always be substituted with the value from the preceding DO command. So my take on BeVee's example is this: L KF +5 T DW 11 DO DW 11 T DW 11 // Executes instruction T DW 5 L KF +1 T DW 11 DO DW 11 T DW 11 // Executes instruction T DW 1 In an ideal world, the programmer would have used "T DW 0" instead of "T DW 11" as this is somewhat the "norm" to indicate indirect addressing in S5's (in fact a 944 CPU from memory requires this and will replace it with a "0"). For the record, the S5 instruction list does indeed state that the operation following a DO command is combined through a logical OR with the parameter specified in the preceding DW or FW and executed. I am reasonably sure though that this is not meant literally. Not too sure where these two conflicting advises leave you in your quest to understand the functionality of the logic, but I hope it helps anyhow (perhaps someone else remembers or knows for sure or has an S5 handy to test it).
	Last edited by: O_Moderator at: 12/8/2011 12:52 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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12/8/2011 5:40 PM	Rate (0)
Simaticus Bronze Member Joined: 1/30/2007 Last visit: 6/3/2022 Posts: 262 Rating: (24)	Hi everybody, the result of this example depends on the cpu you are using. So my take on BeVee's example is this: L KF +5 T DW 11 DO DW 11 T DW 11 // Executes instruction T DW 5 In cpu944 the result will be T DW5, in cpu 941..3 it will be T DW 15. (5 or 11 => 15) L KF +1 T DW 11 DO DW 11 T DW 11 // Executes instruction T DW 1 dito T DW 1 / T DW 11 (1 or 11 => 11) Hence we need to know what cpu you are using. Cheers

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