YouTube - Understanding Modbus Serial and TCP/IP by ProSoft Technology. Published on Feb 12, 2014.

By John Rinaldi of Real Time Automation (YouTube - RealTimeAutomation channel):

• YouTube - All You Need to Know About Modbus RTU Published on Feb 4, 2010.
• YouTube - All You need to know about Modbus TCP Published on Jul 13, 2010.
• YouTube - Serial Communication RS232 & RS485 Published on Feb 21, 2012.
• YouTube - Serial Communication Published on Feb 21, 2012.
• YouTube - Modbus Data Structure Published on Apr 25, 2012.