K
Hallo,
As fire protection flap control and supervision I have developed hardware and software (assembler for a PIC16F877), connected which to ModBus RTU as Slave about via RS485 2 wire, see here:
http://www.domnick-elektronik.de/aktbsk.htm
A MAX232 for a RS232 interface and a SN75176 for a RS485 interface is on the lower circuit board with jumper for the choice of the Rx outputs. With the program ModScan the software runs about RS232 perfectly.
About RS485 it does not run so well because the times of the switchover for sending or restoral on receive are unknown to me. Bits are lost or are moved?
Bytes (CRC) shall pass after reception of the last one according to the ModBus protocol 3.5 bytes to waiting time. In other descriptions I do not find values of at most 4 ms as time out value at 9600 baud again others value of 10...100ms. Does time switch which one the master, (PC about RS232 to a Converter (IC485IP 1) RS232 <---> RS485, the RTS signal switch the Tx on/off and the DCE/DTE switch the Rx on/off.
When I may do the SN75176 of received (Rx) to send (Tx) change?
I must the SN75176 change how fast of again send (Tx) to received (Rx)?
To the better understanding a diagram:
http://www.domnick-elektronik.de/imgakt/modbusdia_1.gif
I have the German text translated with Click & Translate; my English is very bad.
Many thanks for the help.
As fire protection flap control and supervision I have developed hardware and software (assembler for a PIC16F877), connected which to ModBus RTU as Slave about via RS485 2 wire, see here:
http://www.domnick-elektronik.de/aktbsk.htm
A MAX232 for a RS232 interface and a SN75176 for a RS485 interface is on the lower circuit board with jumper for the choice of the Rx outputs. With the program ModScan the software runs about RS232 perfectly.
About RS485 it does not run so well because the times of the switchover for sending or restoral on receive are unknown to me. Bits are lost or are moved?
Bytes (CRC) shall pass after reception of the last one according to the ModBus protocol 3.5 bytes to waiting time. In other descriptions I do not find values of at most 4 ms as time out value at 9600 baud again others value of 10...100ms. Does time switch which one the master, (PC about RS232 to a Converter (IC485IP 1) RS232 <---> RS485, the RTS signal switch the Tx on/off and the DCE/DTE switch the Rx on/off.
When I may do the SN75176 of received (Rx) to send (Tx) change?
I must the SN75176 change how fast of again send (Tx) to received (Rx)?
To the better understanding a diagram:
http://www.domnick-elektronik.de/imgakt/modbusdia_1.gif
I have the German text translated with Click & Translate; my English is very bad.
Many thanks for the help.
