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MODBUS ASCII with a 1500 PLC

Created by: itwasworkingbefore at: 6/22/2023 7:04 AM (4 Replies)

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6/22/2023 7:04 AM

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itwasworkingbefore

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Dear all,

Do you know if it is possible to do a MODBUS ASCII communication with a 1500 PLC? We have the module CM PtP RS232 HF but it seems that it is only capable to handle MODBUS RTU connections.

Modbus ASCII is not very used anymore, but we need it to integrate a chiller in our control system. Unfortunately this chiller only communicates either by cabled IOs, losing a lot of capabilities, or by RS232/485 Modbus ASCII

ASCII mode, messages start with a colon ( : ) character (ASCII 3A hex), and end with a carriage return-line feed (CRLF) pair (ASCII 0D and 0A hex).
The allowable characters transmitted for all other fields are hexadecimal 0 ... 9, A ... F. Networked devices monitor the network bus continuously for the colon character. When one is received, each device decodes the next field (the address field) to find out if it is the addressed device.
Intervals of up to one second can elapse between characters within the message. If a greater interval occurs, the receiving device assumes an error has occurred. A typical message frame is shown below.

Start	Address	Function	Data	LRC	End
:	2 Chars	2 Chars	N Chars	2 Chars	CR LF

Our first option would be not to add a third party gateway.

Thanks in advance!!

Last edited by: Jen_Moderator at: 06/22/2023 09:42:27

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6/22/2023 7:08 AM	Rate (0)
qwazee Platinum Member Joined: 3/30/2020 Last visit: 12/11/2025 Posts: 5656 Rating: (1082)	( How does the topic title fit the subject matter? ) Have a look at the following: Modbus ASCII driver for S7-1200/1500
	Activities of this user is voluntary. There is no obligation or liability placed on this user. Though optional, your 'please' and 'thank you' is highly valued.
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This contribution was helpful to 2 thankful Users Duris_I itwasworkingbefore

6/22/2023 7:30 AM	Rate (0)
Duris_I Diamond Expert Joined: 4/28/2015 Last visit: 11/27/2025 Posts: 10970 Rating: (843)	Hello, one question to OP, I expect better change of Topic name to different to actual because I don't see any logical reason to that actual and your different problem inside your post. Simply any user searching for telnet possibility will find MODBUS ASCII problem within your post, this is not logical, correct?
	Last edited by: Duris_I at: 06/22/2023 07:32:10 With best regards... Ivan Duris Flight: OMICO
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6/22/2023 8:04 AM	Rate (0)
itwasworkingbefore Member Joined: 9/12/2019 Last visit: 8/20/2025 Posts: 7 Rating: (0)	Hello all, I am really sorry for the title of the topic. I don't know why but it got copied from my last post at this forum. The right title for this thread could be "MODBUS ASCII with a 1500 PLC" Sorry again. Regards,
	Last edited by: itwasworkingbefore at: 06/22/2023 08:04:31
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This contribution was helpful to 1 thankful Users Jen_Moderator

6/27/2023 11:10 AM	Rate (0)
itwasworkingbefore Member Joined: 9/12/2019 Last visit: 8/20/2025 Posts: 7 Rating: (0)	Hello! Thanks a lot for your suggestion. I confirm that using that library I managed to get communication with the Chiller talking Modbus ASCII and the PLC S7-1515 using the card CM PTP RS232 HF. For the configuration of the card I chose Freeport/Modbus (not 3964), starting on any character and recognizing message end by timeout. Then a normal call to the FB LModbus_asciiMaster. It is important to declare a struct of the type "LModbus_typeAsciiConfiguration" and configure properly the baud rated, parity and mostly the modeInterfacePTP (all is well explained in the comments). Then use it in the call of the function. Thanks for your support!

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MODBUS ASCII with a 1500 PLC

Created by: itwasworkingbefore at: 6/22/2023 7:04 AM (4 Replies)

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itwasworkingbefore

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MODBUS ASCII with a 1500 PLC

Created by: itwasworkingbefore at: 6/22/2023 7:04 AM (4 Replies)

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itwasworkingbefore

Last edited by: Jen_Moderator at: 06/22/2023 09:42:27

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