Omega PHCN-961, Руководство пользователя, Страница: 34 / 46

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5.11 COMMUNICATION PROTOCOL
1
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Protocol setting
This instrument uses RS-485 communication. It’s can be connected with 1 to 64 instruments
in 2 wires at the same time and communicate with PC. The distance of communication is
around 1200M.
The data form is “N81”(1 start bit, 8 data bits,1 stop bit, NO verify check code)
The baud rate is 300 to 38400 bit/s (usually is 9600 bit/s)
Users have to set the ID(NB) of the instruments and the baud rate(BT) before connecting to
RS-485
BT 0 1 2 3 4 5 6 7
Baud
rate 300 600 1200 2400 4800 9600 19200 38400
Usually, the instrument is in stand by in receiving status. Once it receives the correct ID then
it will send out the data to PC. Finished sending it will enter into receive status again.
To avoid the conflict, each instrument has to use different ID(decided by NB)
All of the instruments and PC must use the same baud rate.(decided by BT)
2
. Data form
All one-word data is from -32767 to +32767, using the hexadecimal number system, the high
bit is sign.
All one-byte is integer.
The data is ASCII code :the start sign is @(40H), the end sign is CR(0DH)
The other data use the ASCII code to express the hexadecimal number system
All data should be between 30H to 39H and 41H to 46H. the instructions are form 51H to
5AH.
Double-byte sending: the low byte is the first, the high byte is the second
One-byte sending: the high nibble is the first, the low nibble is the second.
A full communication form is :40 ,ID, the sequence of the instruction,CRC,0D
The ID is the number of the instrument(NB)
CRC is the Circulation redundant codes verification, it’s the ID code and data codes XOR
result.