Future Design MCT-MC 4.3, User Manual

Page: 141 / 186

MCT-MC
4.3
Appendix - 141 - FDC MCT-MC
Appendix
A.1 Communications
The MC control is equipped with Modbus RTU as its standard protocol. This section is intended to provide the
user with a basic understanding of serial communications and how to interface with the MC. Numbers in the
format “0x00” represent values in hexadecimal. Numbers in the format “0” represent values in decimal.
Numbers in the format “00000000” represent values in binary unless otherwise stated.
A.1.1 Explanation of Terms
Machine-to-Machine Communication
In order for machines to communicate with each other, they need a code called a character format or character
set. They require rules called protocol to govern their conversation and prevent confusion and errors.
Computers need a connecting interface over which to communicate. They may use one pair of wires to send
information in one direction and another pair to send in the opposite direction (full duplex), or they may use one
pair to send data in both directions (half duplex).
Character Format
The code or character format for MC data communications is shared by virtually everyone in the electronics
industry. This code defines a stream of 1’s and 0’s that are created by varying a voltage signal in a regular
manner. This code is the American Standard Code for Information Interchange, called ASCII.
Bits and Bytes
The word “bit” is simply the contraction of the words bi nary digi t . A bit is the basic unit in ASCII. It is either a
“1” or a “0”. A byte is a string of eight bits that a computer treats as a single character. ASCII can use a single
byte to represent each letter of the alphabet, each digit and each punctuation mark we use.
ASCII
The ASCII code defines 128 separate characters, one for each letter, digit and punctuation mark. ASCII also
includes control characters similar to those we find on computer keys, such as backspace, shift and return. It
also has nine communications control characters for identification, enquiry (inquiry), start of text, end of text,
end of transmission, acknowledge, negative acknowledge and escape. The ASCII code is sometimes written
in a base 16 number system that is called hexadecimal or “hex” for short. The numbers 0 through 9 represents
the first ten digits of this system, and the letters A through F represents the final six digits. The 128 ASCII
character codes with the decimal, binary and hexadecimal equivalents are listed in the following table.
ASCII Control Codes
ASCII Control Codes are used to give instructions to the remote device and result in specific actions, such as
a line feed instruction on a printer. ASCII Control Codes, the first 33 ASCII characters (non printable), are
important for the operation of communicating equipment. They give instruction to remote devices that result in
specific actions such as a line feed on a printer. Holding down the keyboard control key while pressing the
appropriate keyboard key is what sends these values.