问题
I'm trying to run this piece of code:
from pymodbus.client.sync import ModbusSerialClient as ModbusClient
import logging
logging.basicConfig()
log = logging.getLogger()
log.setLevel(logging.DEBUG)
client = ModbusClient(method='rtu', baudrate=9600, parity='E', port='/dev/ttyUSB0', timeout=1)
client.connect()
rr = client.read_holding_registers(40000, 7, unit=0x01)
print rr
client.close()
But I get only this:
DEBUG:pymodbus.transaction:Running transaction 1
DEBUG:pymodbus.factory:Factory Response[131]
DEBUG:pymodbus.transaction:adding transaction 0
DEBUG:pymodbus.transaction:getting transaction 1
Exception Response(131, 3, IllegalAddress)
On the other hand this C code (using libmodbus) is working:
modbus_t *mb;
int16_t hregs[9];
mb = modbus_new_rtu('/dev/ttyUSB0', 9600, 'E', 8, 1);
modbus_set_slave(mb, 1);
modbus_read_registers(mb, 0x40000, 7, hregs)
What am I doing wrong?
回答1:
I am assuming you want to read the first seven holding registers. In that case, the address to be given to the read_holding_registers function is 0. The function implicitly adds the offset of 40000 for holding registers.
So, try changing your read code to this
rr = client.read_holding_registers(0, 7, unit=0x01)
回答2:
Exception Response(131, 3, IllegalAddress) means:
A value contained in the query data field is not an allowable value for the slave. This indicates a fault in the structure of remainder of a complex request, such as that the implied length is incorrect. It specifically does NOT mean that a data item submitted for storage in a register has a value outside the expectation of the application program, since the MODBUS protocol is unaware of the significance of any particular value of any particular register.
http://www.simplymodbus.ca/exceptions.htm
[UPDATE]:
Did you try with 0x40000 or 0x400 (as a default in many cases)? 0x40000 (hexadecimal) have different with 40000 (decimal)
来源：https://stackoverflow.com/questions/33264449/pymodbus-exception-response131-3-illegaladdress