Simulating a PLC #73

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1. OrangeTux commented on Aug 27, 2019

   

   OrangeTux

   on Aug 27, 2019

   Last edited by OrangeTux

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   Hello @piertoni,

   Thanks for your question. From what I understand you want the value of a register to be depending on the start address of the request. Am I correct?

   For what I have understood with app.route I can only define one value at a time.

   It is correct that the the handlers should return only 1 value. If a client requests multiple registers than the handler is executed multiple times using a different value for each address.

   But wouldn't something like this work for your?

   @app.route(slave_ids=[1],function_codes=[3], addresses=list(range(0x200,0x215))):
       def producer(slave_id, function_code, address):
           if address == 0x200:
               # prepare all your other registers
   
               regs_word[0x200] = 0xaabb # first registers
               regs_word[0x201] = 0x2231 # prepares other registers
               regs_word[0x202] = 0x231a # prepares other registers
         
        return regs_word[0x200]
2. piertoni commented on Aug 27, 2019

   

   piertoni

   on Aug 27, 2019

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   Hello @piertoni,

   Thanks for your question. From what I understand you want the value of a register to be depending on the start address of the request. Am I correct?

   Exactly, in fact I am replicating the PLC behavior and if I read 16 regs starting from 0x200 I get one string I.E. Producer name, If I read 16 regs starting from 0x201 I get another string I.E. production date. Is not really a standard modbus behavior from my point of view... but is like this 😄

   For what I have understood with app.route I can only define one value at a time.

   It is correct that the the handlers should return only 1 value. If a client requests multiple registers than the handler is executed multiple times using a different value for each address.

   But wouldn't something like this work for your?

   @app.route(slave_ids=[1],function_codes=[3], addresses=list(range(0x200,0x215))):
       def producer(slave_id, function_code, address):
           if address == 0x200:
               # prepare all your other registers
   
               regs_word[0x200] = 0xaabb # first registers
               regs_word[0x201] = 0x2231 # prepares other registers
               regs_word[0x202] = 0x231a # prepares other registers
         
        return regs_word[0x200]

   Yes, this will work better than my code! Thanks!
   It's a hack anyway but for a simulator I think is fine.
   Really thanks!
3. piertoni

   closed this as completedon Aug 27, 2019
4. piertoni commented on Aug 27, 2019

   

   piertoni

   on Aug 27, 2019

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   mmm thinking better I don't know if this (in general) will work because should be something like this:

       @app.route(slave_ids=[1],function_codes=[3], addresses=list(range(0x200,0x215))):
       def producer(slave_id, function_code, address):
           if address == 0x200:
               # prepare all your other registers
   
               regs_word[0x200] = 0xaabb # first registers
               regs_word[0x201] = 0x2231 # prepares other registers
               regs_word[0x202] = 0x231a # prepares other registers
         
        return regs_word[address]
   
       @app.route(slave_ids=[1],function_codes=[3], addresses=list(range(0x201,0x216))):
       def production_date(slave_id, function_code, address):
           if address == 0x201:
               # prepare all your other registers
   
               regs_word[0x200] = 0x1111 # first registers
               regs_word[0x201] = 0x0000 # prepares other registers
               regs_word[0x202] = 0x123b # prepares other registers
         
        return regs_word[address]

   In fact the region are overlapping... I don't think will work, what do you think?
5. piertoni

   reopened this on Aug 27, 2019
6. OrangeTux commented on Aug 27, 2019

   

   OrangeTux

   on Aug 27, 2019

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   It's a hack anyway but for a simulator I think is fine.

   I am not sure if there is a non-hacky option. To be fair, your requirement of having registers values depend on the start address seem a little bit odd for me.

   In fact the region are overlapping... I don't think will work, what do you think?

   I am not exactly how this will work out, but I don't think it will work as you want it to work. At least uModbus is not intended to work that way when I created this package.
7. piertoni commented on Aug 28, 2019

   

   piertoni

   on Aug 28, 2019

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   I am not sure if there is a non-hacky option. To be fair, your requirement of having registers values depend on the start address seem a little bit odd for me.

   Yeah, I agree, that seems odd to me too... but ask Wago producers... 😄

   In fact the region are overlapping... I don't think will work, what do you think?

   I am not exactly how this will work out, but I don't think it will work as you want it to work. At least uModbus is not intended to work that way when I created this package.

   If you think that it is possible to retrieve the length of the request just tell me where to start and eventually I can write the code.
   If not I will close the issue, thank you for uModbus, is cool! 😄
8. OrangeTux commented on Aug 29, 2019

   

   OrangeTux

   on Aug 29, 2019

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   If you think that it is possible to retrieve the length of the request just tell me where to start and eventually I can write the code.

   Assuming you run a Modbus TCP server than you could create your own request handler that extends from the umodbus.server.tcp.RequestHandler. If you than override than the umodbus.server.AbstractRequestHandler.execute_route() you have access to the info you want.