SN75176 CODE FOR sx48
AHMET AKSU
Posts: 62
·are there anybody who has a sample code for a comunication over rs485 with modbus·
AHMET AKSU
Posts: 62
Comments
There is www.sxlist.com that might have something if anything has been done. If not, www.piclist.com may have code that is easily converted to an SX28.
Do you have any sample code in another microprocessor? Even an 8051 or AVR can be revised.
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Post Edited (AHMET AKSU) : 3/5/2008 10:28:45 AM GMT
The sn75176 is driven by the same software for RS-232 serial both in the Modus and in general. SX/B can easily provide you with USART services in software and these connect via Tx and Rx pins to the sn75176. Pins 2 and 3 control the direction of the sn75176 and can be connected together and have on pin control them - recieve would be low and transmit would be high.
In your PIC example, it seems that Driver Enable controls the direction of the sn75176. If you read the documentation for the sn75176, it explains how to properly use the A and B lines. This is not the +12/-12 of RS-232, it is differential voltages. You might read about RS-485 half-duplex to understand it.
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Post Edited (Kramer) : 3/5/2008 1:28:14 PM GMT
· byte 1·· ":"········ this is the start caracter
· byte·2·············· the adres of sx between 1 and 20
··byte·3·············· comand (a number between 1 and 20)
· byte·4 to byte n·· n numbers of data byte which abaut the byte 3
· the final byte : the checksum of the bytes for the transmition control
I·have writen·pc side code to make this.and test vb progam with a industrial temperature controler.I need information abaut the usart of the sx.I want to know which command to transmit ,which comand to receive?
The chip itself is easy to use. Basically, all stations are in "listen" mode (RE/DE pulled low, I believe). When the master wants to talk, RE/DE is taken high and the data is sent to the chip on the D input. The other stations see the data on their R pins.
Now, the MODBUS protocol is a bit complicated, especially the checksum generation. But, you'll only need to implement one or two command sequences and it is possible to hardcode the checksums required. MODBUS is still very popular, despite its age.
Which PLC brand are you trying to communicate with? Some are easier to work with than others.
I think I have some more details which I can dig out when I get home.
Cheers,
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Tom Sisk
http://www.siskconsult.com
·
I see Modbus ASCII requires a 7 bit format with or without parity.· You may have to adapt SERIN and SEROUT to provide the format you want.· It is easier without any parity as that requires a bit of added assembly code, but in assembly code you can have any USART serial format you require.
Download the FREE SX/B documentation and FREE SX-Key IDE v.3.23 to get started.· If you intend to buy an SX-Key, buy the bundle with Guenther's tutorial text as it is quite important.· If you intend to have 262 bytes of SRAM, you will need an SX-48 Protoboard as the SX-28 has roughly half the SRAM and only 2k of program code space.
As mentioned before,·these SRAM registers are far smaller than the Modbus standard. Also, since Modbus addressing is 16 bits, not 8bits - you will possibly use up more registers for handling the addresses too.
Modbus seems very valid for supporting 'legacy systems'. Apparently is was widely used in industrial applications. There is even and Enron Exxon·Modbus that I guess is for oil industry systems.
The SX alone can really only provide a 'mini-slave' due to the SRAM limit. While the Modbus will support 256 nodes, RS-485 is generally limited to 32 nodes.· You mention that you want to provide 20. ·So you may not need a full Modbus register model.
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Post Edited (Kramer) : 3/6/2008 12:11:11 PM GMT
I suspect getting started in SX/B would make this all evolve more quickly. Later, someone can help you set up more serial protocols and parity after you have proved to yourself that the Modbus slave program is working properly. After all, if you don't know how to program in assembly, you might get stuck with the USART and not finish the project.
Why start with a small, but complex detail when you hve a lot to learn?
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1. are there a comand on sxb "select case" like on picbasic
2. can you write basic example for the serout and serin comand if its possible
If your 'new' to RS-485 then this has helped me.
I am working on a project that involves controlling irrigation sprinkler valves. Each one of the valves will be addressable. I started with the following document:
http://www.parallax.com/Portals/0/Downloads/docs/prod/appkit/rs485Communication.pdf
I've attached the *.bs2 code from the example. Next I converted the slave to *.sxb, this is also attached. Was having some problems as the project progressed with the control.bs2 code, early on, so I switched over to a PC running ProComm and used and RS-232 to RS-485 adapter. Then wrote a ProComm script in the 'Aspect' language to control the slave.
Also a good reference is the book by Jan Axelson, 'Serial Port Complete: COM Ports, USB Virtual COM Ports Second Edition' Found my copy on eBay for a good price.
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Mike
Please forgive my error, I thought that an SX/B Manual was completed and available.· That seems to still be pending; so you will have to rely on the HELP screens to explain SX/B.· Jon Williams is working on a text, but only the first two parts are available at this time. There may be a way to print out the SX/B Help screens in a readible fashion, but I have not yet figure out how.· I have preferred to study SASM as it is a very good way to learn assembler.· The code is more compact and generally runs faster.
Regarding 'Select Case' - this is a multiple branching function. IN SX/B, you would use 'IF.... THEN.... ELSE' to do a similar kind of branching. The HELP screens have code examples. While the command's name maybe different, the use is the same. Of course, there will be other differences in programing style. But, it isn't that difficult to adapt if you fully understand the original program.
The fact is, that all fundamental Basic programing functions are functionally quite similar but different products choose to create a different lexicon for their functions.
The SXes support Nibble Swapping in their machine code - the SX/B command is SWAP -·and since I see that Modbus depends on nibbles to compactly transmit hexidecimal numbers, you might find that feature quite handy to even improve on the PIC code.
It isn't very difficult, once you adapt to it. I suspect SX/B may even be simpler as it doesn't have to adapt to the dozens of different chips that PIC makes. Essentially, there are only two hardware types - The SX-18/20/28 type and the SX-48/52 type.
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PLEASE CONSIDER the following:
Do you want a quickly operational black box solution or the knowledge included therein?······
Post Edited (Kramer) : 3/6/2008 4:03:33 PM GMT