schematic for RS 232 to RS 485 converter

is it necessary to check CRC bytes which i get from PC?????????

it is not necessary but its good to check it to avoid any problems. MODBUS rtu uses CRC16. Check the following link:
http://www.ccontrolsys.com/w/How_to_Compute_the_Modbus_RTU_Message_CRC

hey guys,

I am back to this thread...

I am receiving some error while communication with PC using some PC software like modscan.

error is like below.

CRC error in receiving frame.

while when s/w display my data it shown my crc ok but the other data are garbage value.

so what's the problem???

Please give me reply on urgent basis...

Can you explain your problem with some example? Like what you're sending what your pc software (modscan) is receiving. If modscan says your crc is wrong then it must be wrong.

In that case first of all s/w sent me some code for reading of data of slave.
code is as below.
01 04 00 00 00 02 and 2 bytes of CRC
In above code 01-Slave add, 04-Function Code, 00 00-reading add, 00 02- length of data.

Now after receiving of these data i sent back 01 04 04 00 32 00 64 5B A0.
01-slave add, 04-function code, 04-length of data, 00 32 & 00 64- Data, 5B A0- CRC.

in above case i can see CRC in s/w which is as per my code is right.

So what is problem???

CRC is ok.. and byte orientation is also fine. Really not sure whats the problem. make sure you are changing rx/tx of RS485 chip at the right time. I mean after all bytes are sent properly.

Dear Ajay,

Thanks for reply..

When i sent data directly without calculating of CRC it receive perfact data but when i received some data from S/W and then check CRC, after that when i sent my data with calculating of CRC then this problem is occur..

So what's the exact issue is occur?

how can your data be read perfectly without CRC? The software must be checking for CRC. I think there is a problem in understanding.

In first case i am not calculating CRC using Microcontroller but calculate CRC manually and send data with appropriate CRC.

While in second case calculate CRC using Microcontroller and then send data to S/W.