the setting for this is either 1 or 2.
Not always. The Modbus specification declares that the selection of 'no parity' requires two stop bits. Whether a device can be configured for 1 or 2 stop bits is device-specific.
The problem is that a large number of serial implementations on devices can not handle two stop bits with 8 data bits (Modbus RTU is, by definition, an 8 bit data word)
The most common default implementation of serial communications seems to be 8-N-1: 8 data bits, no parity, 1 stop bit. Every device I have used can handle 8-N-1, but there are several devices that could not handle 8-N-2. One slave device had only 8-N-2 for the 'no parity' selection. The master could not do 8-N-2 and the only way to get it to work was even parity for both devices.
RS-485 has its own error checking
I think the statement means to state that the Modbus protocol uses error checking. Modbus RTU uses CRC error checking and Modbus ASCII uses LRC error checking. Either protocol can run on the RS-485 transport layer.
The EIA 485 spec covers stuff like a balanced interface, multidrop topology, bus voltage and common mode limits, unit loading, data rate at various distances.
Error checking at the transport layer level is a parity check . RS-485 is a transport layer, a carrier, a transmission mechanism. As such, it can use parity for error detection when implemented in the form of UART.
Configuration parameter Settings
The settings are made via various methods, depending on the device
- multiposition rotary or DIP switches
- firmware/software selection
- soldered links
The highest grade devices also offer selection of bias resistance and/or termination resistance, usually with hardware like a jumper or DIP switch.
It is not uncommon to find that the network changes are not recognized until power to the device is cycled (turned off, then back on).