Example
Modbus data acquisition
In pvbaddon/daemons/modbus/client/ you find a daemon for modbus that can be configured using an INI file. With USE_SOCKET=0 you will use modbus rtu over a serial line. If USE_SOCKET=1 you would use modbus tcp. Under [CYCLES] we define what we want to read from modbus. In this examples all cycles read from slave 1 and starting address 0. We read a number of 10, 8, 2 and 2 of the according data items.
Steps
example.ini
# ini file for modbus_client # # USE_SOCKET := 1 | 0 # if 0 then USE_TTY # DEBUG := 1 | 0 # BAUDRATE := 300 | # 600 | # 1200 | # 1800 | # 2400 | # 4800 | # 9600 | # 19200 | # 38400 | # 57600 | # 115200 # STOPBITS := 1 | 2 # PARITY := NONE | ODD | EVEN # PROTOCOL := RTU | ASCII # CYCLE:= , # name := coilStatus(slave,adr) | # inputStatus(slave,adr) | # holdingRegisters(slave,adr) | # inputRegisters(slave,adr) # CYCLETIME in milliseconds # SHARED_MEMORY_SIZE must be equal to SHARED_MEMORY_SIZE of pvserver # MAX_NAME_LENGTH is maximum length of variable name in shared memory # [GLOBAL] USE_SOCKET=0 DEBUG=1 CYCLETIME=1000 N_POLL_SLAVE=5 # number of cycles a slave will not be polled when it fails [SOCKET] IP=192.168.1.100 PORT=502 [TTY] DEVICENAME=/dev/ttyUSB0 BAUDRATE=9600 RTSCTS=1 STOPBITS=1 PARITY=NONE PROTOCOL=RTU [RLLIB] MAX_NAME_LENGTH=30 SHARED_MEMORY=/srv/automation/shm/modbus1.shm SHARED_MEMORY_SIZE=65536 MAILBOX=/srv/automation/mbx/modbus1.mbx [CYCLES] NUM_CYCLES=4 CYCLE1=10,inputStatus(1,0) CYCLE2=8,coilStatus(1,0) CYCLE3=2,holdingRegisters(1,0) CYCLE4=2,inputRegisters(1,0)
Modbus register map
Within rlModbus all data addresses in Modbus messages are referenced to 0, with the first occurrence of a data item addressed as item number zero. Further, a function code field already specifies which register group it operates on (i.e. 0x, 1x, 3x, or 4x reference addresses).
0xxxx Read/Write Discrete Outputs or Coils.
1xxxx Read Discrete Inputs.
3xxxx Read Input Registers.
4xxxx Read/Write Output or Holding Registers.