modbus RTU timeout

Using the modbus RTU slave-master examples, reading holding registers is OK, while writing holding registers does not work with baud rate lower or equal to 9600 baud.

Working conditions:

• Eltima virtual port driver
• any baudrate without strict baudrate emulation
• baudrate > 9600 with or without strict baudrate emulation

Non working conditions:

• Eltima virtual port driver
• baudrate <= 9600 with strict baudrate emulation