In Modbus ASCII, no binary sequence is transmitted, but ASCII code. This makes it directly readable by humans, but the data throughput is lower compared to RTU.
Is very similar to RTU, but TCP/IP packets are used to transmit the data. TCP port 502 is reserved for Modbus/TCP. Modbus/TCP has been defined in the IEC 61158 standard since 2007.
Remote Terminal Unit is a very common field bus and transmits the data in binary form. This ensures a good data throughput.
However, the data cannot be evaluated directly by humans, but must first be converted into a readable format.
Specific information is also available at www.modbus.org