Lack of IllegalAddress error while reading from not existing holding registers

[symygy]

I am trying to create simple SerialModbusServer using pymodbus library and then I want to read some not exisiting registers. I expect getting a modbus "Illegal Data Address" error but as I understand it correctly I'm getting "Slave Device Failue":
DEBUG:pymodbus.logging:Processing: 0xf1 0x80 0x4 0x40 0x30

Can anyone explain what am I doing wrong? I was also trying to use ModbusSequentialDataBlock but with similat results.
I am using that simple script to get required serial ports:
import virtualserialports virtualserialports.run(2, loopback=False, debug=True)

PS I was really trying to show my code in a proper code block using editor but I always ended up like this:

Server code:
`def run_server():
nreg = 200
hr_data = {i: 17 for i in range(nreg)}

store = ModbusSlaveContext(
    di=ModbusSparseDataBlock({i: 15 for i in range(nreg)}),
    co=ModbusSparseDataBlock({i: 16 for i in range(nreg)}),
    hr=ModbusSparseDataBlock(hr_data),  # tylko adresy 0-199
    ir=ModbusSparseDataBlock({i: 18 for i in range(nreg)})
)

context = ModbusServerContext(slaves=store, single=True)

StartSerialServer(
    context=context,
    port=com_port, 
    baudrate=9600,
    bytesize=8,
    parity="N",  
    stopbits=1,
    timeout=1
)

`

Client code:
`def test_virtual_device():
client = ModbusSerialClient(port="/dev/pts/3", baudrate=9600, bytesize=8, parity="N", stopbits=1)

try:
    print("\n--- Reading register 1000 ---")
    result = client.read_holding_registers(address=1000, count=5, slave=1)

    if result.isError():
        print("error", result)`

[janiversen]

Not sure I understand what you want, a server do not read data.

You do not write which version of the library you use, so I assume it is the newest.

If you refer to the client, then the reason is probably that you did not define slave 1 in the server. Did you try to to read valid data first ? Normally you would get illegal address if the slave is correct.

[symygy]

Yes, I tried to read i.e. register 100 and it was ok, I got proper value. But when I am trying to read register 1000 (which does not exists) I got Slave Device Failure instead of Invalid Data Address.

result = client.read_holding_registers(address=100, count=5, slave=1) - OK
result = client.read_holding_registers(address=1000, count=5, slave=1) - I am expecting Illegal Data Address, I have Slave Device Failure instead

My library version is 3.9.2

[janiversen]

Seems like a bug, pull requests are welcome.