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SILVESTROS
Joined: 30 Dec 2016
Posts: 2
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| MODBUS SLAVE WITH PIC |
 Posted: Fri Dec 30, 2016 1:47 pm |
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Hello to all.
I try to send some characters with Modbus protocol (bus type RS-485), to an 4X20 LCD, that I connected with a PIC16F887. The pic works as slave, while I use as master a master emulator (ComTestPro) to send data to make some tests first, and later I'll use a PLC. Communication with pic is ok, Modbus commands 01,02,03 work fine, but I've a problem with write data to pic registers and send that to LCD.
I'm new in pic programming, so I don't know how to address pic registers, what kind of variable I must use, and how to send that var. to LCD to display a character. The LCD accepts var. types as PrintString, PrintAscii, PrintNumber. LCD works fine when I use PrintString " ", but when I use the var. that I used at MB com. 06 (write single register), LCD shows 0 or 0x00.
Thanks in advance for any help or advice. |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19369
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| Posted: Fri Dec 30, 2016 2:11 pm |
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Standard Modbus registers are int16.
Generate a string.
| Code: |
char temp_str[17]; //assuming a 16 char LCD
sprintf(temp_str,"%lu", register_variable);
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Obviously the 'register_variable' will need to be the same one you use in the Modbus code.
Once the string is generated, this can be sent with your printstring function.
If you are a slave, you need to _read_ the register. Master writes, slave reads. |
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SILVESTROS
Joined: 30 Dec 2016
Posts: 2
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| Posted: Sun Jan 01, 2017 8:30 am |
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Thanks Ttelmah for info.
About modbus slave code, because pic is the slave, do you mean that first I must use Write Single Register function (06), after Read Single Register (03) and then send the string to LCD , or the opposite? Is it possible to send me a sample code for generating the string to PrintString command for LCD?
Many thanks in advance, and happy New Year. |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19369
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| Posted: Sun Jan 01, 2017 9:12 am |
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| No, you said you wanted to 'write some data to PIC registers'. If the Modbus master is sending data to the PIC, then the PIC has to read this. |
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