CHAPTER 4
COMMUNICATION PROTOCOLS
4-1
DC-24 and DC-25 operation manual
4.
COMMUNCATION PROTOCOLS
In this paragraph, the different protocols will be explained, as well as the programmation
of the displays through them. The formats of values of the numbers and characters are
written in this manual are:
•
When telling about a hexadec
imal number, this will be followed by an “h”.
•
When telling about a decimal number, this will be followed by a “d”.
•
When telling about a binary number, this will be followed by a “b”.
•
When telling about an ASCII character, this will be explained in the context.
As an example, the X ASCII character can be explained as 58h, 88d or 1011000b, as
needed in the moment. Number 15 ASCII can be seen as 31h 35h, 49d 53d or 110001d
110101d.
4.1.
ASCII protocol for RS-485
This protocol allows communicating with any device that disposes serial line and can
configure the communication protocol, as a PC or PLC. There can be 99 devices connected to
the net with the corresponding amplifiers every 30 devices.
Using this protocol forces the display to work on slave mode. This means that the display
waits for a message and, once verified, it responds depending on the command received.
To understand how to configure the protocol, the used terms are used
Message.
It is formed by all the necessary characters to establish the dialogue. For each
correct message received, the display returns a response message. The message consists of
three parts: The header, the data and the end of block
Header.
It is used to identify the beginning of the message. The character @ (64d, 40h)
followed by the address of the display is sent.
Data block:
The data block can consist of commands or responses. The valid commands
are the following
The command
PT
is a request to the display to ask for the current temperature and
humidity values.
The command
VT
is an order to the display to shoe temperature and humidity values that
are sent.
End of block: It is used to identify the complete arrival of the block. It is used the character “Carry
return” (13d 0Dh)
