Examples

This chapter illustrates with some examples, how working with the Modbus Bridge looks like. The bytes that are sent via LoRaWAN are presented here as hex strings, while on the air they are sent as raw bytes. Modbus Commands and Responses are broken down to their parts in the explanations, but explaining the format used by Modbus in detail is beyond the scope of this manual. You can find a short explanation on Modbus on Wikipedia: https://en.wikipedia.org/wiki/Modbus.

Uplinks in Verbose Payload Format (PlFmt=1)

The following shows some examples of configuration for the automated reading and what the generated Uplinks for that could look like.

Example A1: Read Holding Registers 0, 1, and 2 of device with address 1

Verbose Payload Format (Port 3, PlFmt=1)

MbCmd = '010300000003'

# Example resulting Uplink after successful readout
Up, Port 3: '005d1698fd0c0103061234567890ab000003'
 '005d1698fd' -> timestamp = 1561762045 -> 2019-06-28T22:47:25 UTC
 '0c'       -> first Response is 12 bytes long
 '0103061234567890ab000003' 12 bytes modbus response:
   '01' -> slave device with address 1
   '03' -> function 3 = read Holding Register, success
   '06' -> 6 bytes of data in Response following
   '1234567890ab' -> 6 bytes of data
   '0000' -> start reading at register 0
   '03' -> read 3 consecutive registers

# Example resulting Uplink after failing readout
Up, Port 3: '005d1698fd0601830b000003'
 '005d1698fd' -> timestamp = 1561762045 -> 2019-06-28T22:47:25 UTC
 '06'       -> first Response is 6 bytes long
 '01830b000003' 3 bytes modbus response:
   '01' -> slave device with address 1
   '83' -> function 3 with error indicator 80 = read Holding Register, failed
   '0b' -> error code 11: "Gateway Target Device Failed to Respond"
   '0000' -> start reading at register 0
   '03' -> read 3 consecutive registers

Example A2: Read coils 1000-1019 of device 32

Verbose Payload Format (Port 3, PlFmt=1)

MbCmd = '200103e80014'

# Example resulting Uplink
Up, Port 3: '005d1698fd 09 200103f1041a03e814'
 '005d1698fd' -> timestamp = 1561762045 -> 2019-06-28T22:47:25 UTC
 '09' -> first Response is 9 bytes long
 '200103f1041a03e814' 9 bytes of response:
  '20' -> slave device with address 32
  '01' -> read coils, success
  '03' -> 3 bytes of data
  'f1041a' -> 20 bits of data packed into 3 bytes
  '03e8' -> start reading at coil 1000
  '14' -> read 20 consecutive coils

Example A3: Read registers from two devices

Verbose Payload Format (Port 3, PlFmt=1)

MbCmd = '0a0300010005,3001ea600020'

# Example resulting Uplink
Up, Port 3: '005d1698fd100a030a111122223333444455550001050a30010412345678ea6020'
 '005d1698fd' -> timestamp = 1561762045 -> 2019-06-28T22:47:25 UTC
 '10' -> first Response is 16 bytes long
 '0a030a11112222333344445555000105' 16 bytes of Response
  '0a' -> slave device with address 10
  '03' -> read Holding Registers, success
  '0a' -> 10 bytes of data following
  '11112222333344445555' 10 bytes of data
  '0001' -> start reading at register 1
  '05' -> read 5 registers
 '0a' -> second Response is 10 bytes long
 '30010412345678ea6020' 10 bytes of Response
  '30' -> slave device with address 48
  '01' -> read Coils, success
  '04' -> 4 bytes of data following
  '12345678' -> 32 bits of data packed in 4 bytes
  'ea60' -> start at coil 60000
  '20' -> read 32 coils

Example A4: Split uplink message

Verbose Payload Format (Port 3, PlFmt=1)

MbCmd = '010300010020'
# Command reads 32 consecutive registers resulting in 64 bytes payload

# Example resulting Uplinks for a Spreading Factor of 12 with 51 bytes of payload per message
Up 1, Port 3: '005d1698fd46010340000100020003000400050006000700080009000a000b000c000d000e000f001000110012001300140015'
  '005d1698fd' -> timestamp = 1561762045 -> 2019-06-28T22:47:25 UTC
  '46' -> first Response is 70 bytes long since the remainder of the message does not contain 70 bytes,
  you know there must be an additional part coming
Up 2, Port 5: '0016001700180019001a001b001c001d001e001f00200120'
  This contains the rest of the message. Appended to the previous message, it adds up to the correct number of bytes.

Uplinks triggered by Downlink Commands

Example B1: Read single Input Register by Downlink

Verbose Payload Format (Port 4, Downlink Response)

Down, Port 4: '06180401000001'
 '06' -> first Command is 6 bytes long
 '180401000001' 6 bytes of Modbus Command
  '18' -> slave device with address 24
  '04' -> function 4, read Input Register
  '0100' -> start at register 256 '0001' -> read 1 register

# Example resulting Uplink
Up, Port4: '004b3dd67508180402abcd010001'
 '004b3dd675' -> timestamp = 1262343797 -> 2010-01-01T11:03:17 UTC
 '08' -> first Response is 8 bytes long
 '180404abcd010001' 8 bytes of Response
  '18' -> slave device with address 24
  '04' -> read Input Register, success
  '02' -> 2 bytes of data following
  'abcd' -> 2 bytes of data
  '0100' -> start at register 256
  '01' -> read 1 register

Example B2: Writing holding registers on multiple devices

Verbose Payload Format (Port 4, Downlink Response)

Down, Port 4: '06a106aabb12340fa210a0010004081122334455667788'
 '06' -> first Command is 6 bytes long
 'a106aabb1234' 6 bytes of Modbus Command
  'a1' -> slave device with address 161
  '06' -> function 6, write single Holding Register
  'aabb' -> address of Register to write = 43707
  '1234' -> two bytes of data
 '0f' -> second Command is 15 bytes long
 'a210a0010004081122334455667788' 15 byte of Modbus Command
  'a2' -> slave device with address 162
  '10' -> function 16, write multiple Holding Registers
  'a001' -> start at register 40961
  '0004' -> 4 registers to write
  '08' -> 8 bytes of data follow
  '1122334455667788' -> 8 bytes of data

# Example resulting Uplink Up, Port 4: '004b3dd67506a1860200000006a210a0010004'
 '004b3dd675' -> timestamp = 1262343797 -> 2010-01-01T11:03:17 UTC
 '06' -> first Response is 3 bytes long
 'a18602000000' 3 bytes of Modbus Response
  'a1' -> slave device address 161 '86' -> write single Holding Regsiter, failed
  '02' -> error code 2: "Illegal Data Address"
  '0000' -> start register not used (undefined)
  '00' -> count not used (undefined)
 '06' - second Response is 6 bytes long
 'a210a0010004' 6 bytes of Modbus Response
  'a2' -> slave device address 162
  '10' -> write multiple Holding Registers, success
  'a001' -> start at register 40961
  '0004' -> 4 registers to write

Uplinks in Compact Payload Format

Example C1: Single Modbus Command, PlFmt 4

Example C2: Multiple Commands, PlFmt 5

Example C3: Multimple Commands, leading in multiple Upoads, PlFmt 5