Register offset and Modbus Error Code bug

[aliihsancengiz]

Hello , recently found a bug about register offset and modbus error codes.
Register Offset(u8regsize) is a uint8_t variable, you cannot exceed address range 255.

When ever you try to read a address(uint16_t) out of the this range , address is down casted to uint8_t and compared to table size in order to decide whether read address is exceeded this range.

Example case:

Register Table size 250.
Intended register read adress is 2000.
In that case we expect an EXC_ADDR_RANGE error code but we got successfull reading.

Modbus Frames decomposition

But if we want to read register at offset 509.

Modbus Frames decomposition