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slow communication with cp341

Created by: gre_m at: 10/10/2010 5:44 PM (6 Replies)

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10/10/2010 5:44 PM	Rate (0)
gre_m Posts: 947 Rating: (45)	I'm looking for a bottleneck. I have a micro-pc sends 41 bytes in СPU317-2pn/dp (firmware 2.6.7) every 20ms,CPU317-2pn/dp must pass every 20ms 17byte in micro-pc. I use ASCII protocol 57600baud on RS232. I have obtained the transfer (from cpu)of only about once every 50..60ms - I look at the oscilloscope. If micro-pc nothing passes, the transfer of CPUin 20 ms is obtained. I assumed that the bottleneck is the k-bus. although I may be wrong software programmer CP341. My programm work in OB35 with period 20ms I would also like to know - when the CPUwork with CP: after OB1 or at another time
gre_m Posts: 947 Rating: (45)
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10/11/2010 7:13 AM	Rate (0)
cgarcia Posts: 8 Rating: (0)	Hi, In our implementation of MODBUS for CPU 417 & CP 443-1, presents the same problem. Indeed as you note the problem is due to the delays associated with the K-Bus which requires multiple machine cycles for process AG_LSEND/LRECV functions. My recommendation is that you try to use your communication routines in OB1 or in a OB that will allow shorter cycle times. Another option is to use ethernet and AG_SRECV / AG_SSEND blocks (check if your CPU supports it). Greetings
cgarcia Posts: 8 Rating: (0)	Last edited by: cgarcia at: 10/11/2010 7:14 AM
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10/11/2010 7:59 AM	Rate (0)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 3/20/2025 Posts: 3042 Rating: (1061)	Hello gre_m to start with, cgarcia's K-Bus related conclusion is NOT really applicable to you (a 400 has a "real" K-Bus which is used for user data, a 300 uses the P-Bus as advised HERE). I do however agree with cgarcia's recommendation to use Ob1 for the call of comms blocks to speed things up (assuming OB1's scan time is faster than your OB35 related call rate of 20ms). Having said that, based on Appendix 2 of the CP 341 Point-to-Point Communication, Installation and Parameter Assignment manual you can expect that it'll take 26ms for the transmission of one 50 Byte long message@ 57600baud. 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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10/11/2010 5:54 PM	Rate (0)
gre_m Posts: 947 Rating: (45)	Hello, all! based on Appendix 2 of the CP 341 Point-to-Point Communication, Installation and Parameter Assignment manual I expect take less 13ms for the transmission of one 17 Byte long message @ 57600baud. Really, I have 55 .. 60ms. I tried to put communications in OB1. Improvements are not seen. And this is understandable: the duration Ob35 about 17ms.OB1 suspended(interrupted)OB35 and its duration is 3ms - which I think is not enough for communication. On the other hand, I do not know - whether I'm doing when it calls FB7, FB8: Is it possible to make them call in the OB twice per cycle formake positive edgeon REQ, or we need to do it in different cycles. In PtP Software not find sample for duplexcommunication CP341 by ASCII. On the one hand in the manual is written: CPU 3xx makes the communication after OB1, on the other side for PtP-based communications is not as it seems, because these blocks use sfc58 or sfb52 for later version, which seems to be executed immediately. Can I get the materials management Wed through ports on the bus: With sfc58 I would record the buffer in CP341, then run it's Excuse my English
gre_m Posts: 947 Rating: (45)
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10/11/2010 7:13 PM	Rate (1)
Kaulquappe Posts: 3093 Rating: (324)	Hello gre_m, depending on the used blocks of the library, the data transfer between CPU and CP is either executed at the end of OB1 (e.g. PUT, GET) or immediatelly when the block is called (e.g. P_SND_RK, P_RCV_RK). With CP341 maximum 14 bytes can be transferred from the CPU to the CP, and 14 bytes from the CP to the CPU in one cycle (The user doesn't see/recognize that). So the shorter your cycle time is, the more data can be transferred. When you know that your cycle time is high, I recommend to call P_SND_RK and P_RCV_RK in OB35. P_SND_RK and P_RCV_RK must be called only once per CP. To realize a full duplex communication with the ASCII-driver a simultaneous call of P_SND_RK and P_RCV_RK is necessary/possible. Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (324)
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10/12/2010 5:29 PM	Rate (0)
gre_m Posts: 947 Rating: (45)	Thank you! tell me, please- where I can read these details? I think that 14 bytes - this is not enough. For 2-cycle I've read 51 bytes.
gre_m Posts: 947 Rating: (45)
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10/12/2010 6:00 PM	Rate (0)
Kaulquappe Posts: 3093 Rating: (324)	Hello gre_m, in the 341 manual, section 6.3.1 you can find the following information: "The data transmission is initiated by a positive edge at the REQ input. A data transmission operation can run over several calls (program cycles), depending on the amount of data involved." And the same in section 6.3.2 for P_RCV_RK: "A data transmission operation can run over several calls (program cycles), depending on the amount of data involved." The manual doesn't offer information about the number of bytes transferred in one cycle. Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (324)
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