How to calculate CRC16 checksum for iButton

[mech962784]

Dear Andre

i need the sample code for implementing modbus slave on a PIC16F877A

please help me

[Andre_Pretorius]

here is the code i used on a 16f627
Hope it helps

[mech962784]

Dear Andre

thank you for the code you have posted,actually i am trying to use the PIC16F877A

another thing i have copy and pasted your code to proton+ compiler and i got some error messages one of them was
for this part of the code:

IF CRC16.Bit0=1 Then '<------ error here is saying Invalid Cast for this type of variable
CRC16=$A001^(CRC16>>1)
Else
CRC16=CRC16>>1
EndIF

i don't know what does that means,please help me.

Best Regards

[Ioannis]

First of all this is PBP forum list not Proton.

Second, as this is PBP, all examples are for this compiler. The syntax is a little different.

The syntax of the line IF CRC16.Bit0=1 Then means: Set bit 0 of the word variable CRC16.

You have to open your manual and find how this can be accomplished in your Compiler.

Ioannis

[mech962784]

Daer Andre
can you please post the circuit schematic for such code?

i want to know what is the use for the
PORTB.4 = 1
PORTB.5 = 0

any clue?

best regards

[Andre_Pretorius]

Have you read the document emplementing modbus on serial comms,
You can get it at www.modbus.org

[mech962784]

Dear Andre

yes i have the modbus specification.

but these pins or at least PortB.5 is not something related to the specification,i think it is related to RS485 handshaking (correct me if i am wrong).

is it correct?and which pin it is connected to?