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Code Review: LAR2 Any pointer addressing

Created by: GLMnet at: 1/25/2010 2:10 PM (11 Replies)

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1/25/2010 2:10 PM	Rate (0)
GLMnet Posts: 3 Rating: (0)	Hi, I'm new with this language and have a question about memory addressing. In short: what this code does? TAR2 AD DW#16#FFFFFF L P##Send_Buffer +D LAR1 Send_Buffer is a string located in an instance DB, i.e. it is on the STAT of this FB. I understand that AD DW#16#FFFFFF is taking the address and not the type of the "any pointer" in TAR2 and adding to a "local address" for Send_Buffer. I remember making the program fail when trying to P## an STAT variable, and it worked with a TEMP variable without the TAR2 thing. Now I think it is adding the base address of the Instance DB with the offset address of the STAT variable. Is this OK? And How does TAR2 has the base address of the DB? I could not find the program being setting LAR2 anywhere. Thank you.
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1/26/2010 8:54 AM	Rate (0)
Remark Bronze Member Joined: 9/1/2006 Last visit: 5/3/2023 Posts: 192 Rating: (12)	Hi GLM, This is what happens.... In short: what this code does? TAR2 // Get pointer from AR2 -> points to start of instance data record AD DW#16#FFFFFF // Mask the lower 24-bits (let through only pointer part) L P##Send_Buffer // get the address (offset) to the Send_buffer record (STAT-var?) +D // add address offset LAR1 // load pointer AR1 -> Send_buffer How does AR2 point to the instance ? This is standard procedure for an FB (thats why it's not wise to use AR2 yourself inside a FB) Before the actual FB call is made, the AR2 is assigned to the start of the instance data. Often this is 0.0 (only in case of multiple instances you will find other values pointing to the offset of an instance). best regards, Remark
	Last edited by: O_Moderator at: 5/6/2010 1:17 PM
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This contribution was helpful to 3 thankful Users Brogettenks PLCnoob Grégori Fernandes...

1/26/2010 1:30 PM	Rate (0)
GLMnet Posts: 3 Rating: (0)	This is a great answer. Thank you.
GLMnet Posts: 3 Rating: (0)
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7/12/2020 7:22 PM	Rate (0)
sstan1020 Advanced Member Joined: 11/15/2015 Last visit: 3/23/2023 Posts: 21 Rating: (0)	Hi, Here have an actual example that show you how to call and use at DI instance. Hope can solve your problem. First picture is the result. Attachment 1 Result MAPPING AND EQUAL.png (69 Downloads)

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7/12/2020 7:25 PM	Rate (0)
sstan1020 Advanced Member Joined: 11/15/2015 Last visit: 3/23/2023 Posts: 21 Rating: (0)	Attachment 2 Attributes setting.png (52 Downloads)

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7/12/2020 7:26 PM	Rate (0)
sstan1020 Advanced Member Joined: 11/15/2015 Last visit: 3/23/2023 Posts: 21 Rating: (0)	Attachment 2_1 FB CALL.png (44 Downloads)

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7/12/2020 7:29 PM	Rate (0)
sstan1020 Advanced Member Joined: 11/15/2015 Last visit: 3/23/2023 Posts: 21 Rating: (0)	Attachment 3 Ltest Para Setting.png (45 Downloads)

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7/12/2020 7:31 PM	Rate (0)
sstan1020 Advanced Member Joined: 11/15/2015 Last visit: 3/23/2023 Posts: 21 Rating: (0)	Attachment 4 Ltest Programming Get Address2.png (54 Downloads)

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7/12/2020 7:31 PM	Rate (0)
sstan1020 Advanced Member Joined: 11/15/2015 Last visit: 3/23/2023 Posts: 21 Rating: (0)	Attachment 5 Ltest pokeblk.png (37 Downloads)

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7/12/2020 7:32 PM	Rate (0)
sstan1020 Advanced Member Joined: 11/15/2015 Last visit: 3/23/2023 Posts: 21 Rating: (0)	Attachment 6 UDT DEFINITION.png (42 Downloads)

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