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RS-485 Communication in PIC16F887 controller

 
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CHANDRU1991ECE



Joined: 03 Feb 2021
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RS-485 Communication in PIC16F887 controller
PostPosted: Mon Feb 15, 2021 10:56 pm     Reply with quote

Hello guys,

I need to communicate a microcontroller PIC 16F887 with my PC via modbus RTU/485.

I am using MASIBUS RS-485 Converter and MODSCAN Software for testing purpose.

When i start communicating and i am receiving message as follows, RECEIVED INVALID RESPONSE TO MODBUS QUERY.

Can you help me???
temtronic



Joined: 01 Jul 2010
Posts: 7975
Location: Greensville,Ontario

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PostPosted: Tue Feb 16, 2021 5:56 am     Reply with quote

re:
Quote:
When i start communicating and i am receiving message as follows, RECEIVED INVALID RESPONSE TO MODBUS QUERY.

it says ,to me, that something sent a MODBUS 'query' and what was returned was an 'invalid response'. That could mean 'data out of range' but without knowing what the 'query' was , and the actual 'response', I can't say why it happened.

WHICH device reports this error ? The PC or the PIC ?
What PIC program are you using ? Perhaps the CCS RS485 example ?
Ttelmah



Joined: 11 Mar 2010
Posts: 16935

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PostPosted: Tue Feb 16, 2021 7:59 am     Reply with quote

It's the classic 'uninformative' message... Sad

If you search for MODSCAN and this error, you will see that almost every
fault will give it. Incorrect cabling, incorrect baud rate, incorrect register
number etc. etc.. So you need to look at each in turn and see which is wrong.
Some packages do have a proper 'error number' available, which will give
much more information. You need to investigate to see if one does exist.
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