Micromod MOD: MODBUS RTU Communications Guide Manual de usuario descargar pdf (Pagina 14)

MODBUS RTU

COMUNICATIONS GUIDE

USING MODBUS MODULES:

MODULE LOCATION

The sockets in which the module is installed determines its Port number

Table 4. MOD30ML and Modcell MLP Port Numbers

Port Number MOD30ML Modcell MLP

1 Built-In, Slots 9-10 or 10 Slots 31-32 or 32

2 Slots 7-8 or 8 Slots 29, 28-28, 30 or 29-30

3 not available Slots 25-26, 26, 26-27, 27, 27-28 or 28

THE RS-485’S TERM (MASTER/SLAVE) SWITCH

• The master is responsible for stabilizing the bus

• In the YES position the module provides this master function by pulling the comm+ line high and

the comm- line low, each through 560Ω resistors

• Some PC cards have these resistors built in, generally only on the receiver. This works fine in 4-

wire mode if the transmitter does not tri-state, or in 2-wire mode. 4- wire mode, with a tri-stating

transceiver, may require a module to have its switch in the master position, even if its not acting

as the master.

THE COM DEFAULTS SWITCH

• If the MOD30 ML or Modcell MLP configuration is unknown, setting this switch to th eYES position

will allow communications with the unit at 9600 baud, no parity, 8 data bits and 1 stop bit. After

downloading the desired parameters, remove power, COM DEFAULTS switch to NO and power

up.

THE HIGH AND LOW SWITCHES

• Set the MODBUS Address

• The High switch sets the first hexadecimal digit of the address, and the Low switch sets the

second. For example, a switch setting of 13 hex represents a decimal address of 19.

The 2-wire RS-485 module has no switches. It must be configured by the Application Builder software, to

change the factory defaults. The factory defaults are 9600 baud, no parity, 8 data bits, one stop bit and a

MODBUS address of one. Do not connect an unconfigured module to a network if there is another device on

the network with address one.

1 2 ... 9 10 11 12 13 14 15 16 17 18 19 ... 31 32

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Micromod MOD: MODBUS RTU Communications Guide Manual de usuario Pagina 14