Eurotech PCN-1001, User Manual

Page: 89 / 118

Test
an RS485 connection and use the RS485_GUI PCN-1001 User manual
89
PCN-1001_UserMan_En_4.0
Broadcast Message
Each message between Master and Slave is made in the following format:
Source Destination TotalPacketNumber PacketNumber DataLength
Source: Address of the device transmitting the message
Destination: Address of the target device
TotalPacketNumber: Quantity of Packets to be sent
PacketNumber:
The number of the current packet being sent
DataLength: Length of the data in this Packet [0x01 to 0xFE or MAX]
Therefore, as we can see from the examples on the previous pages, a message may take this form:
[0x01, 0x02, 3, 2, MAX]
In this case Node “0x01” is sending a message to Node “0x02”; this is package 2 of 3, and is MAX (255)
characters long. Whereas:
[0x02, 0x01, 1, 1, 2]
would be Node “0x02” is sending a message to Node “0x01”; this is package 1 of 1, and is 2 characters long.
The following message would be a Broadcast message:
[0xFF, 1, 1, 1, 2]
This is indicated by the 0xFF, which means all Slave devices will act upon the message, however, no reply will be
sent by any of the Slave devices.
The DATA field
All the messages exchanged between the Master and the Slave units have to be encapsulated in the SNP
transmission.
The command to send is contained in the Data field of the SNP protocol.
All the commands are formed by: the Command string, the String terminator, and some values (Value 1, Value 2,
…). Each value can be a number (1, 2 or 4 bytes long ) or a string.
The Data field maximum length is contained in the MAX_DATA_LENGTH
The Data field is formed by:
NAME
LENGTH (BYTES) CONTENTS
Command string
0-256 bytes Command
String terminator
1 0
Value 1 1,2,4 First parameter
Value 2 1,2,4 Second parameter
….
1,2,4 ….
Send Message
Part 3
[‘S’, ‘J’, 3, 3, x]
Received by all
Systems