title: Does Modbus RTU require a gap between characters when transmitting?
body: <p>I'm a little confused about the inter-character gap in Modbus and whether its required when a master sends a message to a slave.  The protocol spec says you can't have more than a 3.5 character gap between bytes when transmitting but is there any specific minimum amount of time you must have between bytes?</p>
  
  <p>I've written a Modbus driver (master) that is able to communicate with a variety of devices and most don't seem to care about any gap between characters when receiving messages. However, I've come across a couple of devices where I was unable to communicate reliably without putting in a some kind of delay (measured in microseconds) between bytes, which is determined by the baud rate.</p>
  
  <p>Is the character gap an absolute requirement or does it depend on the manufacture of the device and how the implement the Modbus protocol?</p>