RS485, Modbus & NVT

api.rs485Send(msg)

Overview

Sends msg to RS485 bus.

Turn on RS485 using rs485State first.

Arguments

• msg (string) - Data to be sent to RS485 bus

Example

--sends 'test' string to RS485
api.rs485Send('test')

api.rs485Setup(baudrate, parity, stopBits, dataBits)

Overview

Change the configuration of RS485 interface.

Arguments

• baudrate (integer) - Baudrate to use for communication (up to 921600 baud)
• parity (integer) - Parity, 0 for none, 1 for odd and 2 for even parity
• stopBits (integer) - Number of stop bits, 1 or 2 allowed
• dataBits (integer) - Number of data bits, 7 or 8 allowed

Example

--setup RS485 interface to 9600 Baud, 8E1
api.rs485Setup(9600, 2, 1, 8)

api.rs485State(state)

Overview

Turns on the RS485 circuitry.

Must be used before rs485Send or rs485Receive.

Arguments

• state (integer) - New state of RS485 circuitry: 0 for off, 1 for on (fast power-up)

Example

api.rs485State(0) --turn off RS485

api.rs485Receive(timeout)

Overview

Waits timeout milliseconds for data reception from RS485 bus.

Turn on RS485 using rs485State() function first.

After the first character is received the inter-character delay is 10ms. If the inter-character delay needs to be longer the function should be called again.

Arguments

• timeout (integer) - The maximum time in milliseconds to wait for RS485 device answer

Return

• answer (string) - Data received from RS485 bus in given time
• len (integer) - Number of bytes received

Example

--waits 1s for answer from RS485 bus
ans,len = api.rs485Receive(1000)

api.modbusCrc(msg)

Overview

Calculates Modbus request checksum.

Arguments

• msg (string) - Modbus request

Return

• crc (string) - Modbus crc for request

Example

--calculate checksum for Modbus request 110100010002
req = pack.pack('<b6', 0x11,0x01,0x00,0x01,0x00,0x02)
crc = api.modbusCrc(req) --crc = "EE9B"

api.nvtProcess(buf)

Overview

Processes NVT message and either sets baudrate, datasize, parity or stop size for MBUS or MODBUS.

Arguments

• buf (string) - Message to be processed

Return

• msg (string) - Message without NVT sequence
• answer (string) - NVT answer

Example

-- If massage received (buf) send it to RS485
ret,port,buf = api.loraSend(0,1000,data)
if buf ~= nil then
	buf, nvtans = api.nvtProcess(buf)
	api.rs485Send(buf)
end

api.nvtEncode(msg)

Overview

Encodes message to NVT format

Arguments

• msg (string) - Message to be encoded to NVT

Return

• answer (string) - NVT message

Example

ans,len = api.rs485Receive(50)
ans = api.nvtEncode(ans)
api.loraSend(0,1,ans)